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1.  Continental variation in relative hippocampal volume in birds: the phylogenetic extent of the effect and the potential role of winter temperatures 
Biology letters  2005;1(3):330-333.
Hippocampal (HC) volume has been hypothesized to increase with an increase in food-hoarding specialization in corvids and parids. Recent studies revealed that (i) the HC/hoarding relationship is significant when a difference in HC volume between Eurasian and North American species is controlled for and (ii) the evolutionary association has been acting on a broader phylogenetic context involving avian families outside the Corvidae and Paridae. However, the phylogenetic extent of the continent effect has not been previously addressed. Using data representing 48 avian species, we performed a phylogenetic analysis to test if continental effects are important in a wider evolutionary spectrum. Our results support the observation that Eurasian species have generally larger HC than North American species if variation in food hoarding, which also varied between continents, was held constant. Surprisingly, the relationship between continental distribution and relative HC volume was significant when we included only non-hoarding families in our analysis, indicating that the extent of the continent effect is much broader than originally described. We investigated the potential role of minimal winter temperatures at the northernmost distribution borders in mediating continent effects. The effect of winter temperatures on HC volume was weak and it did not vary consistently along continents. We suggest that the general continental differences in relative HC size are independent of food hoarding and that its determinants should be sought among other ecological factors and life-history traits.
doi:10.1098/rsbl.2005.0328
PMCID: PMC1523380  PMID: 16878181
Corvidae; food caching; hippocampus; Paridae; phylogeny
2.  Pregnancy weight gain: marmoset and tamarin dads show it too 
Biology letters  2006;2(2):181-183.
Paternal behaviour is critical for the survival of offspring in many monogamous species. Common marmoset (Callithrix jacchus) and cotton-top tamarin (Saguinus oedipus) fathers spend as much or more time caring for infants than mothers. Expectant males of both species showed significant increases in weight across the pregnancy whereas control males did not (five consecutive months for marmoset males and six months for cotton-top tamarin males). Expectant fathers might be preparing for the energetic cost of fatherhood by gaining weight during their mate’s pregnancy.
doi:10.1098/rsbl.2005.0426
PMCID: PMC1483903  PMID: 16810338
weight gain; paternal care; couvades; primates
3.  Pregnancy weight gain: marmoset and tamarin dads show it too 
Biology Letters  2006;2(2):181-183.
Paternal behaviour is critical for the survival of offspring in many monogamous species. Common marmoset (Callithrix jacchus) and cotton-top tamarin (Saguinus oedipus) fathers spend as much or more time caring for infants than mothers. Expectant males of both species showed significant increases in weight across the pregnancy whereas control males did not (five consecutive months for marmoset males and six months for cotton-top tamarin males). Expectant fathers might be preparing for the energetic cost of fatherhood by gaining weight during their mate's pregnancy.
doi:10.1098/rsbl.2005.0426
PMCID: PMC1483903  PMID: 16810338
weight gain; paternal care; couvade; primates
4.  Continental variation in relative hippocampal volume in birds: the phylogenetic extent of the effect and the potential role of winter temperatures 
Biology Letters  2005;1(3):330-333.
Hippocampal (HC) volume has been hypothesized to increase with an increase in food-hoarding specialization in corvids and parids. Recent studies revealed that (i) the HC/hoarding relationship is significant when a difference in HC volume between Eurasian and North American species is controlled for and (ii) the evolutionary association has been acting on a broader phylogenetic context involving avian families outside the Corvidae and Paridae. However, the phylogenetic extent of the continent effect has not been previously addressed. Using data representing 48 avian species, we performed a phylogenetic analysis to test if continental effects are important in a wider evolutionary spectrum. Our results support the observation that Eurasian species have generally larger HC than North American species if variation in food hoarding, which also varied between continents, was held constant. Surprisingly, the relationship between continental distribution and relative HC volume was significant when we included only non-hoarding families in our analysis, indicating that the extent of the continent effect is much broader than originally described. We investigated the potential role of minimal winter temperatures at the northernmost distribution borders in mediating continent effects. The effect of winter temperatures on HC volume was weak and it did not vary consistently along continents. We suggest that the general continental differences in relative HC size are independent of food hoarding and that its determinants should be sought among other ecological factors and life-history traits.
doi:10.1098/rsbl.2005.0328
PMCID: PMC1523380  PMID: 16878181
Corvidae; food caching; hippocampus; Paridae; phylogeny
6.  Surfing in tortoises? Empirical signs of genetic structuring owing to range expansion 
Biology Letters  2013;9(3):20121091.
Much of our current knowledge about the genetic dynamics in range expansions originates from models, simulations and microcosm experiments that need to be corroborated by field data. Here, we report a neutral genetic pattern that matches the predictions of the genetic surfing theory. Genetic surfing occurs when repeated founding events and genetic drift act on the wave of advance of an expanding population, promoting strong spatial structure. In the range expansion of the tortoise Testudo graeca from North Africa to southeastern Spain, we found several genetic signatures consistent with surfing: a decrease of genetic diversity with distance from the initial founder area, clinal patterns in allele frequencies, rare African alleles which have become common at distal sites in the Spanish range, and stronger spatial differentiation in the expanded range than in the original one. Our results provide support for the theory that genetic drift can be an important force in shaping the genetic structure of expanding populations.
doi:10.1098/rsbl.2012.1091
PMCID: PMC3645018  PMID: 23554278
genetic drift; rare alleles; founding events; isolation-by-distance; spur-thighed tortoise
7.  Goffin cockatoos wait for qualitative and quantitative gains but prefer ‘better’ to ‘more’ 
Biology Letters  2013;9(3):20121092.
Evidence for flexible impulse control over food consumption is rare in non-human animals. So far, only primates and corvids have been shown to be able to fully inhibit the consumption of a desirable food item in anticipation for a gain in quality or quantity longer than a minute. We tested Goffin cockatoos (Cacatua goffini) in an exchange task. Subjects were able to bridge delays of up to 80 s for a preferred food quality and up to 20 s for a higher quantity, providing the first evidence for temporal discounting in birds that do not cache food.
doi:10.1098/rsbl.2012.1092
PMCID: PMC3645019  PMID: 23485873
delay of gratification; food exchange; impulse control; avian cognition
8.  Odour cues influence predation risk at artificial bat roosts in urban bushland 
Biology Letters  2013;9(3):20121144.
Odours that accumulate from roosting can attract predators and increase predation risk. Consequently, selection should favour strategies that allow prey to evade detection by predators, including changing roosts. Insectivorous bats that roost in tree hollows regularly switch roosts and roost in different sized groups, strategies that would alter the accumulation of roost odours and are hypothesized to reduce predation risk. We experimentally manipulated the amount and refresh rate of roosting odour cues at 90 artificial bat roosts in Sydney, Australia, to test the hypothesis that odours increase predator visitation. Predators visited roosts with bat faeces significantly more often than untreated control roosts. Roosts with small amounts of faeces mimicking sites used by solitary bats had the greatest rate of visitation. This suggests that bats roosting alone, rather than in groups, have a greater likelihood of disturbance or predation. Roost switching probably decreases the predictability of finding occupied roosts; however, we show that all roosts (those currently or recently occupied) were visited by predators, suggesting generalist urban predators readily investigate potential roosts. This is the first demonstration that bat odours are attractive to predators that use olfactory cues, showing that bats are at risk of predation in visually cryptic roosts.
doi:10.1098/rsbl.2012.1144
PMCID: PMC3645020  PMID: 23637390
bat roost; predation risk; urban ecology; Rattus rattus; nest predation
9.  Forests as promoters of terrestrial life-history strategies in East African amphibians 
Biology Letters  2013;9(3):20121146.
Many amphibian lineages show terrestrialization of their reproductive strategy and breeding is partially or completely independent of water. A number of causal factors have been proposed for the evolution of terrestrialized breeding. While predation has received repeated attention as a potential factor, the influence of other factors such as habitat has never been tested using appropriate data or methods. Using a dataset that comprises 180 amphibian species from various East African habitats, we tested whether species occurring in different habitats show different patterns of terrestrialization in their breeding strategy. We recovered a significant association between terrestrialized breeding strategies and forest habitats. In general, forest seems to act as a facilitator, providing a permissive environment for the evolution of terrestrialized breeding strategies. However, while terrestrial oviposition is strongly correlated with lowland and montane forest habitat, complete terrestrial development is significantly correlated with montane forest only, indicating different selective pressures acting at different steps towards complete terrestrial development.
doi:10.1098/rsbl.2012.1146
PMCID: PMC3645021  PMID: 23536440
direct development; Eastern Arc Mountains; reproductive mode; topography; viviparity
10.  Parasitoid wasps influence where aphids die via an interspecific indirect genetic effect 
Biology Letters  2013;9(3):20121151.
Host–parasite interactions are a key paradigm for understanding the process of coevolution. Central to coevolution is how genetic variation in interacting species allows parasites to evolve manipulative strategies. However, genetic variation in the parasite may also be associated with host phenotype changes, thereby changing the selection on both species. For instance, parasites often induce changes in the behaviour of their host to maximize their own fitness, yet the quantitative genetic basis for behavioural manipulation has not been fully demonstrated. Here, we show that the genotype of the parasitoid wasp Aphidius ervi has a significant effect on where its aphid host Acyrthosiphon pisum moves to die following parasitism, including the likelihood that the aphid abandons the plant. These results provide a clear example of an interspecific indirect genetic effect whereby the genetics of one species influences the expression of a specific behavioural trait in another.
doi:10.1098/rsbl.2012.1151
PMCID: PMC3645022  PMID: 23576776
parasitoid; indirect genetic effects; interspecific indirect genetic effects; coevolution; pea aphid
11.  Maintenance of essential amino acid synthesis pathways in the Blattabacterium cuenoti symbiont of a wood-feeding cockroach 
Biology Letters  2013;9(3):20121153.
In addition to harbouring intestinal symbionts, some animal species also possess intracellular symbiotic microbes. The relative contributions of gut-resident and intracellular symbionts to host metabolism, and how they coevolve are not well understood. Cockroaches and the termite Mastotermes darwiniensis present a unique opportunity to examine the evolution of spatially separated symbionts, as they harbour gut symbionts and the intracellular symbiont Blattabacterium cuenoti. The genomes of B. cuenoti from M. darwiniensis and the social wood-feeding cockroach Cryptocercus punctulatus are each missing most of the pathways for the synthesis of essential amino acids found in the genomes of relatives from non-wood-feeding hosts. Hypotheses to explain this pathway degradation include: (i) feeding on microbes present in rotting wood by ancestral hosts; (ii) the evolution of high-fidelity transfer of gut microbes via social behaviour. To test these hypotheses, we sequenced the B. cuenoti genome of a third wood-feeding species, the phylogenetically distant and non-social Panesthia angustipennis. We show that host wood-feeding does not necessarily lead to degradation of essential amino acid synthesis pathways in B. cuenoti, and argue that ancestral high-fidelity transfer of gut microbes best explains their loss in strains from M. darwiniensis and C. punctulatus.
doi:10.1098/rsbl.2012.1153
PMCID: PMC3645023  PMID: 23515978
mutualism; termite; genome degradation
12.  The role of bacteriocins as selfish genetic elements 
Biology Letters  2013;9(3):20121173.
Bacteria produce a wide arsenal of toxic compounds in order to kill competing species. Bacteriocins, protein-based toxins produced by nearly all bacteria, have generally been considered a ubiquitous anti-competitor strategy, used to kill competing bacterial strains. Some of these bacteriocins are encoded on plasmids, which also code for closely linked immunity compounds (thereby rendering toxin producing cells immune to their own toxin). However, the production of bacteriocins can also be interpreted as a means to promote plasmid stability by preferentially selecting for cells carrying the plasmid. If, for example, a cell were to lose the plasmid, it would no longer produce the immunity compound and would be killed by its bacteriocin-producing clone mates. In this respect, bacteriocins can be regarded as similar to previously described toxin–antitoxin systems that are able promote the stable transmission of plasmids to daughter cells. In order to test this prediction, we carried out an experimental evolution study using the bacterium Escherichia coli, finding that bacteriocins can indeed select for the stable maintenance of plasmids. This suggests that bacteriocins can act primarily as selfish genetic elements promoting their own transmission in the population, which may help explain their unique ecology and evolution.
doi:10.1098/rsbl.2012.1173
PMCID: PMC3645024  PMID: 23616642
colicins; experimental evolution; toxin–antitoxin system; addiction complex; post-segregational killing
13.  Emperor penguin body surfaces cool below air temperature 
Biology Letters  2013;9(3):20121192.
Emperor penguins Aptenodytes forsteri are able to survive the harsh Antarctic climate because of specialized anatomical, physiological and behavioural adaptations for minimizing heat loss. Heat transfer theory predicts that metabolic heat loss in this species will mostly depend on radiative and convective cooling. To examine this, thermal imaging of emperor penguins was undertaken at the breeding colony of Pointe Géologie in Terre Adélie (66°40′ S 140° 01′ E), Antarctica in June 2008. During clear sky conditions, most outer surfaces of the body were colder than surrounding sub-zero air owing to radiative cooling. In these conditions, the feather surface will paradoxically gain heat by convection from surrounding air. However, owing to the low thermal conductivity of plumage any heat transfer to the skin surface will be negligible. Future thermal imaging studies are likely to yield further insights into the adaptations of this species to the Antarctic climate.
doi:10.1098/rsbl.2012.1192
PMCID: PMC3645025  PMID: 23466479
metabolic heat loss; thermal imaging; thermoregulation; Antarctic
14.  Predator–prey body size relationships when predators can consume prey larger than themselves 
Biology Letters  2013;9(3):20121193.
As predator–prey interactions are inherently size-dependent, predator and prey body sizes are key to understanding their feeding relationships. To describe predator–prey size relationships (PPSRs) when predators can consume prey larger than themselves, we conducted field observations targeting three aquatic hemipteran bugs, and assessed their body masses and those of their prey for each hunting event. The data revealed that their PPSR varied with predator size and species identity, although the use of the averaged sizes masked these effects. Specifically, two predators had slightly decreased predator–prey mass ratios (PPMRs) during growth, whereas the other predator specialized on particular sizes of prey, thereby showing a clear positive size–PPMR relationship. We discussed how these patterns could be different from fish predators swallowing smaller prey whole.
doi:10.1098/rsbl.2012.1193
PMCID: PMC3645026  PMID: 23536441
gape limitation; individual interaction; ontogenetic niche shift; size dependence; terrestrial–aquatic
15.  Sexual selection hinders adaptation in experimental populations of yeast 
Biology Letters  2013;9(3):20121202.
Sexual selection, the suite of processes that lead to differential mating success among individuals, probably influences the evolutionary trajectory of populations. Because sexual selection often shifts traits away from their survival optima, strong sexual selection pressures are thought to increase potential for population extinction, especially during environmental change. Sexual selection pressures may also increase the opportunity for speciation by accelerating the generation of pre-zygotic isolation among populations. These relationships remain largely untested experimentally. Here, we allow populations of baker's yeast, Saccharomyces cerevisiae, to evolve for approximately 250 generations with altered sex ratios in order to test the effect of the strength of sexual selection on the fate of populations. We find that populations experiencing stronger sexual selection are less able to adapt to a novel environment compared with populations experiencing weaker sexual selection or no sex, and that strong sexual selection erases the benefits of sexual reproduction. This pattern persists when fitness is assayed in a closely related environment. We also identify a trend that may suggest the beginning of pre-zygotic isolation between populations experiencing stronger sexual selection, though this is not statistically significant. These results highlight the importance of sexual selection in shaping macroevolutionary patterns and biodiversity.
doi:10.1098/rsbl.2012.1202
PMCID: PMC3645027  PMID: 23485874
sexual selection; Saccharomyces cerevisiae; extinction; experimental evolution; adaptation
16.  Unusual anal fin in a Devonian jawless vertebrate reveals complex origins of paired appendages 
Biology Letters  2013;9(3):20130002.
Jawed vertebrates (gnathostomes) have undergone radical anatomical and developmental changes in comparison with their jawless cousins (cyclostomes). Key among these is paired appendages (fins, legs and wings), which first evolved at some point on the gnathostome stem. The anatomy of fossil stem gnathostomes is, therefore, fundamental to our understanding of the nature and timing of the origin of this complex innovation. Here, we show that Euphanerops, a fossil jawless fish from the Devonian, possessed paired anal-fin radials, but no pectoral or pelvic fins. This unique condition occurs at an early stage on the stem-gnathostome lineage. This condition, and comparison with the varied condition of paired fins in other ostracoderms, indicates that there was a large amount of developmental plasticity during this episode—rather than a gradual evolution of this complex feature. Apparently, a number of different clades were exploring morphospace or undergoing multiple losses.
doi:10.1098/rsbl.2013.0002
PMCID: PMC3645028  PMID: 23576777
Devonian; vertebrate; paired fin; stem-gnathostome; Endeiolepis
17.  The behavioural and genetic mating system of the sand tiger shark, Carcharias taurus, an intrauterine cannibal 
Biology Letters  2013;9(3):20130003.
Sand tiger sharks (Carcharias taurus) have an unusual mode of reproduction, whereby the first embryos in each of the paired uteri to reach a certain size (‘hatchlings’) consume all of their smaller siblings during gestation (‘embryonic cannibalism’ or EC). If females commonly mate with multiple males (‘behavioural polyandry’) then litters could initially have multiple sires. It is possible, however, that EC could exclude of all but one of these sires from producing offspring thus influencing the species genetic mating system (‘genetic monogamy’). Here, we use microsatellite DNA profiling of mothers and their litters (n = 15, from two to nine embryos per litter) to quantify the frequency of behavioural and genetic polyandry in this system. We conservatively estimate that nine of the females we examined (60%) were behaviourally polyandrous. The genetic mating system was characterized by assessing sibling relationships between hatchlings and revealed only 40 per cent genetic polyandry (i.e. hatchlings were full siblings in 60% of litters). The discrepancy stemmed from three females that were initially fertilized by multiple males but only produced hatchlings with one of them. This reveals that males can be excluded even after fertilizing ova and that some instances of genetic monogamy in this population arise from the reduction in litter size by EC. More research is needed on how cryptic post-copulatory and post-zygotic processes contribute to determining paternity and bridging the behavioural and genetic mating systems of viviparous species.
doi:10.1098/rsbl.2013.0003
PMCID: PMC3645029  PMID: 23637391
polyandry; monogamy; adelphophagy
18.  Evolution of the temporal persistence of immune protection 
Biology Letters  2013;9(3):20130017.
The evolution of resistance to parasites has been the focus of numerous theoretical studies and several mechanisms, ranging from innate to acquired immune responses, have been considered. Life-history theory predicts that long-lived species should invest more resources into maintenance and immunity than short-lived species. Here, we provide further theoretical and empirical support for this hypothesis. First, an analysis of the evolution of the persistence of immune protection in a theoretical framework accounting for maternal transfer of immunity reveals that longer-lived hosts are expected to invest in more persistent intragenerational and transgenerational immune responses. Controlling for phylogenetic structure and for the confounding effect of catabolic activity, we further showed that immunoglobulin half-life and longevity are positively correlated in mammal species. Our study confirms that persistence of immunity has evolved as part of elaborate anti-parasitic defence strategies.
doi:10.1098/rsbl.2013.0017
PMCID: PMC3645031  PMID: 23485875
host–parasite interactions; life-history theory; immune system; maternal antibodies
19.  Asymmetry in pay-off predicts how familiar individuals respond to one another 
Biology Letters  2013;9(3):20130025.
Familiarity influences individual decision-making in many vertebrate species. Here, we propose that familiarity modulates behaviour to different extents depending on the social context of the interaction. Specifically, the more that one player stands to gain relative to the other, the less important familiarity will be in influencing their responses to one another. We test this prediction using pairs of male guppies (Poecilia reticulata) in three competitive scenarios of increasing asymmetry in outcome to the two players: schooling under potential threat (similar outcomes), competing for a defensible food source (some asymmetry) and competing for a receptive female (strongly asymmetrical outcomes). Males show a graded response as asymmetry increases, with familiarity producing marked behavioural differences under potential threat, minor changes when competing for food, but none at all in competition for mating opportunities. This suggests that mutualistic benefits can arise as a by-product of selfish behaviour, supporting the role of pseudo-reciprocity in the evolution of cooperation.
doi:10.1098/rsbl.2013.0025
PMCID: PMC3645032  PMID: 23576778
reciprocity; fish; by-product mutualism; decision-making
20.  Sibling competition and hunger increase allostatic load in spotted hyaenas 
Biology Letters  2013;9(3):20130040.
Allostatis is the process of maintaining homeostatis through behavioural or physiological responses to challenges, and its cumulative energetic cost is termed allostatic load. The allostatic load hypothesis predicts that hunger and the mechanisms that establish and maintain social dominance should have a strong impact on allostatic load. In spotted hyaenas, dominance between twin siblings emerges during intense early competition for maternal milk and involves trained winner/loser effects. Conflict over access to teats declines with age as behavioural dominance conventions are established. In young litters, the allostatic load of subordinates measured in terms of faecal glucocorticoid metabolite concentrations (fGMCs) should be higher than that of dominants. When low milk provisioning threatens survival, hungry subordinates are more assertive, particularly when competing against a dominant sister. Dominants challenged by assertive subordinates should have allostatic loads and fGMCs above those of dominants with subordinates that adhere to dominance conventions. We show that in young litters, subordinates had significantly higher fGMCs than dominants, and dominant sisters had significantly higher fGMCs than dominant brothers. When hungry, both dominants and subordinates had significantly higher fGMCs than when fed. Our results provide evidence that hunger and sibling competition affect allostatic load in spotted hyaenas.
doi:10.1098/rsbl.2013.0040
PMCID: PMC3645033  PMID: 23616643
sibling competition; glucocorticoids; allostatic load; stress; spotted hyaena
21.  Climate warming and the potential extinction of fig wasps, the obligate pollinators of figs 
Biology Letters  2013;9(3):20130041.
Figs (Ficus) have a reciprocally obligate mutualism with tiny, short-lived (1–2 days) fig wasps (Agaonidae). The small size and short life of these pollinators is expected to make them more vulnerable to climate change than their larger and longer-lived hosts. We experimentally tested the thermal tolerances of four species of adult female fig wasp from equatorial Singapore. The results suggest that an increase of 3°C or more above the current temperatures experienced across much of the equatorial tropics would markedly decrease the active adult lifespan of all four species. Fig plants are the centre of an intricate web of specialist and generalist animals. Unless fig wasps can acclimate or adapt to warmer temperatures in time, these responses may disrupt the mutualism, potentially affecting multiple trophic levels.
doi:10.1098/rsbl.2013.0041
PMCID: PMC3645034  PMID: 23515979
climate warming; fig wasps; Ficus; mutualism; thermal tolerance
22.  Riding the crimson tide: mobile terrestrial consumers track phenological variation in spawning of an anadromous fish 
Biology Letters  2013;9(3):20130048.
When resources are spatially and temporally variable, consumers can increase their foraging success by moving to track ephemeral feeding opportunities as these shift across the landscape; the best examples derive from herbivore–plant systems, where grazers migrate to capitalize on the seasonal waves of vegetation growth. We evaluated whether analogous processes occur in watersheds supporting spawning sockeye salmon (Oncorhynchus nerka), asking whether seasonal activities of predators and scavengers shift spatial distributions to capitalize on asynchronous spawning among populations of salmon. Both glaucous-winged gulls and coastal brown bears showed distinct shifts in their spatial distributions over the course of the summer, reflecting the shifting distribution of spawning sockeye salmon, which was associated with variation in water temperature among spawning sites. By tracking the spatial and temporal variation in the phenology of their principal prey, consumers substantially extended their foraging opportunity on a superabundant, yet locally ephemeral, resource. Ecosystem-based fishery management efforts that seek to balance trade-offs between fisheries and ecosystem processes supported by salmon should, therefore, assess the importance of life-history variation, particularly in phenological traits, for maintaining important ecosystem functions, such as providing marine-derived resources for terrestrial predators and scavengers.
doi:10.1098/rsbl.2013.0048
PMCID: PMC3645035  PMID: 23554279
marine-derived nutrients; subsidy; phenological tracking; ecosystem-based management; phenological diversity; resource wave
23.  Cross-cultural variation in women's preferences for cues to sex- and stress-hormones in the male face 
Biology Letters  2013;9(3):20130050.
Women in the UK prefer the faces of men with low levels of the stress hormone cortisol, and the relationship is moderated by the sex hormone testosterone. In a Latvian sample, however, women's preferences were not affected by cortisol, and the interaction with testosterone differed from that of the UK. To further explore cross-cultural variation in preferences for facial cues to sex- and stress-hormones, we tested the preferences of women from 13 countries for facial composites constructed to differ in combinations of the hormones. We found significant relationships between a measure of societal development (the United Nations human development index 2011) and preferences for cues to testosterone in the face, and the interaction between preferences for cues to testosterone and cortisol. We also found a significant relationship between preferences for cues to testosterone and a societal-level measure of parasite stress. We conclude that societal-level ecological factors influence the relative value of traits revealed by combinations of sex- and stress-hormones.
doi:10.1098/rsbl.2013.0050
PMCID: PMC3645036  PMID: 23536442
stress-linked immunocompetence handicap; cortisol; testosterone; face; attractiveness; masculinity
24.  Recurrent functional divergence of early tetrapod keratins in amphibian toe pads and mammalian hair 
Biology Letters  2013;9(3):20130051.
Amphibians have invaded arboreal habitats multiple times independently during their evolution. Adaptation to these habitats was nearly always accompanied by the presence or appearance of toe pads, flattened enlargements on tips of fingers and toes that provide adhesive power in these environments. The strength and elasticity of the toe pad relies on polygonal arrayed cells ending in nanoscale projections, which are densely packed with cytoskeletal proteins. Here, we characterized and determined the evolutionary origin of these proteins in the toe pad of the tree frog Hyla cinerea. We created a subtracted cDNA library enriching genes that are expressed in the toe pad, but nowhere else in the toe. Our analyses revealed five alpha keratins as main structural proteins of the amphibian toe pad. Phylogenetic analyses show that these proteins belong to different keratin lineages that originated in an early tetrapod ancestor and in mammals evolved to become the major keratin types of hair. The ancestral keratins were probably already expressed in areas that required skin reinforcement in early tetrapods, and subsequently diverged to support fundamentally different adaptive structures in amphibians and mammals.
doi:10.1098/rsbl.2013.0051
PMCID: PMC3645037  PMID: 23485876
amphibia; toe pad; keratins
25.  Queen control of a key life-history event in a eusocial insect 
Biology Letters  2013;9(3):20130056.
In eusocial insects, inclusive fitness theory predicts potential queen–worker conflict over the timing of events in colony life history. Whether queens or workers control the timing of these events is poorly understood. In the bumble-bee Bombus terrestris, queens exhibit a ‘switch point’ in which they switch from laying diploid eggs yielding females (workers and new queens) to laying haploid eggs yielding males. By rearing foundress queens whose worker offspring were removed as pupae and sexing their eggs using microsatellite genotyping, we found that queens kept in the complete absence of adult workers still exhibit a switch point. Moreover, the timing of their switch points relative to the start of egg-laying did not differ significantly from that of queens allowed to produce normal colonies. The finding that bumble-bee queens can express the switch point in the absence of workers experimentally demonstrates queen control of a key life-history event in eusocial insects. In addition, we found no evidence that workers affect the timing of the switch point either directly or indirectly via providing cues to queens, suggesting that workers do not fully express their interests in queen–worker conflicts over colony life history.
doi:10.1098/rsbl.2013.0056
PMCID: PMC3645038  PMID: 23637392
Bombus; eusocial insect; life history; queen control; switch point

Results 1-25 (1930)