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1.  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
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; couvade; primates
3.  The origin of mitochondria in light of a fluid prokaryotic chromosome model 
Biology Letters  2006;3(2):180-184.
Biologists agree that the ancestor of mitochondria was an α-proteobacterium. But there is no consensus as to what constitutes an α-proteobacterial gene. Is it a gene found in all or several α-proteobacteria, or in only one? Here, we examine the proportion of α-proteobacterial genes in α-proteobacterial genomes by means of sequence comparisons. We find that each α-proteobacterium harbours a particular collection of genes and that, depending upon the lineage examined, between 97 and 33% are α-proteobacterial by the nearest-neighbour criterion. Our findings bear upon attempts to reconstruct the mitochondrial ancestor and upon inferences concerning the collection of genes that the mitochondrial ancestor possessed at the time that it became an endosymbiont.
doi:10.1098/rsbl.2006.0582
PMCID: PMC2375920  PMID: 17251118
genomics; hydrogenosomes; lateral gene transfer; microbial evolution; endosymbiosis; Magnetococcus
4.  Differential influence of Pomphorhynchus laevis (Acanthocephala) on brain serotonergic activity in two congeneric host species 
Biology Letters  2006;3(1):68-71.
The physiological mechanisms by which parasites with complex life cycles manipulate the behaviour of their intermediate hosts are still poorly understood. In Burgundy, eastern France, the acanthocephalan parasite Pomphorhynchus laevis inverses reaction to light in its amphipod host Gammarus pulex, but not in Gammarus roeseli, a recent invasive species. Here, we show that this difference in manipulation actually reflects a difference in the ability of the parasite to alter brain serotonergic (5-HT) activity of the two host species. Injection of 5-HT in uninfected individuals of both host species was sufficient to inverse reaction to light. However, a difference in brain 5-HT immunocytochemical staining levels between infected and uninfected individuals was observed only in G. pulex. Local adaptation of the parasite to the local host species might explain its inability to manipulate the behaviour and nervous system of the invasive species.
doi:10.1098/rsbl.2006.0583
PMCID: PMC2373828  PMID: 17443968
host manipulation; 5-HT; Gammarus spp.; biological invasion
5.  A two-headed reptile from the Cretaceous of China 
Biology Letters  2006;3(1):80-81.
A malformed embryonic or neonate choristoderan reptile from the Lower Cretaceous Yixian Formation of northeastern China is described. The tiny skeleton exhibits two heads and two necks, with bifurcation at the level of the pectoral girdle. In a fossil, this is the first occurrence of the malformation known as axial bifurcation, which is well known in living reptiles.
doi:10.1098/rsbl.2006.0580
PMCID: PMC2373827  PMID: 17443971
Choristodera; fossil; malformation; axial bifurcation; Cretaceous; China
6.  Reproducing lizards modify sex allocation in response to operational sex ratios 
Biology Letters  2006;3(1):47-50.
Sex-allocation theory suggests that selection may favour maternal skewing of offspring sex ratios if the fitness return from producing a son differs from that for producing a daughter. The operational sex ratio (OSR) may provide information about this potential fitness differential. Previous studies have reached conflicting conclusions about whether or not OSR influences sex allocation in viviparous lizards. Our experimental trials with oviparous lizards (Amphibolurus muricatus) showed that OSR influenced offspring sex ratios, but in a direction opposite to that predicted by theory: females kept in male-biased enclosures overproduced sons rather than daughters (i.e. overproduced the more abundant sex). This response may enhance fitness if local OSRs predict survival probabilities of offspring of each sex, rather than the intensity of sexual competition.
doi:10.1098/rsbl.2006.0579
PMCID: PMC2373826  PMID: 17443963
Amphibolurus muricatus; environmental sex determination; sex ratio; temperature-dependent sex determination
7.  Interspecific transmission of endosymbiotic Spiroplasma by mites 
Biology Letters  2006;3(1):23-25.
The occurrence of closely related strains of maternally transmitted endosymbionts in distantly related insect species indicates that these infections can colonize new host species by lateral transfer, although the mechanisms by which this occurs are unknown. We investigated whether ectoparasitic mites, which feed on insect haemolymph, can serve as interspecific vectors of Spiroplasma poulsonii, a male-killing endosymbiont of Drosophila. Using Spiroplasma-specific primers for PCR, we found that mites can pick up Spiroplasma from infected Drosophila nebulosa females and subsequently transfer the infection to Drosophila willistoni. Some of the progeny of the recipient D. willistoni were infected, indicating successful maternal transmission of the Spiroplasma within the new host species. However, the transmission rate of the infection from recipient flies to their offspring was low, perhaps due to low Spiroplasma density in the recipient flies.
doi:10.1098/rsbl.2006.0577
PMCID: PMC2373825  PMID: 17443956
Drosophila nebulosa; Drosophila willistoni; host–parasite associations; Macrocheles; Spiroplasma poulsonii
8.  Changes in body temperature influence the scaling of V˙O2max and aerobic scope in mammals 
Biology Letters  2006;3(1):99-102.
Debate on the mechanism(s) responsible for the scaling of metabolic rate with body size in mammals has focused on why the maximum metabolic rate (V˙O2max) appears to scale more steeply with body size than the basal metabolic rate (BMR). Consequently, metabolic scope, defined as V˙O2max/BMR, systematically increases with body size. These observations have led some to suggest that V˙O2max and BMR are controlled by fundamentally different processes, and to discount the generality of models that predict a single power-law scaling exponent for the size dependence of the metabolic rate. We present a model that predicts a steeper size dependence for V˙O2max than BMR based on the observation that changes in muscle temperature from rest to maximal activity are greater in larger mammals. Empirical data support the model's prediction. This model thus provides a potential theoretical and mechanistic link between BMR and V˙O2max.
doi:10.1098/rsbl.2006.0576
PMCID: PMC2373824  PMID: 17443976
metabolic rate; allometry; metabolic theory
9.  No evidence of inbreeding avoidance in a polygynous ungulate: the reindeer (Rangifer tarandus) 
Biology Letters  2006;3(1):36-39.
In polygynous species, mate choice is an integrated part of sexual selection. However, whether mate choice occurs independently of the genetic relatedness among mating pairs has received little attention, although inbreeding may have fitness consequences. We studied whether genetic relatedness influenced females' choice of partner in a highly polygynous ungulate—the reindeer (Rangifer tarandus)—in an experimental herd during two consecutive rutting seasons; the herd consisting of 75 females in 1999 and 74 females in 2000 was exposed to three 4.5-year-old adults and three 1.5-year-old young males, respectively. The females' distribution during peak rut was not influenced by their genetic relatedness with the dominant males of the mating groups. Further, genetic relatedness did not influence the actual choice of mating partner. We conclude that inbreeding avoidance through mating group choice as well as choice of mating partner, two interconnected processes of female mate choice operating at two different scales in space and time, in such a highly female-biased reindeer populations with low level of inbreeding may not occur.
doi:10.1098/rsbl.2006.0575
PMCID: PMC2373823  PMID: 17443960
relatedness; mate choice; inbreeding avoidance; Rangifer tarandus
10.  The adaptive significance of ontogenetic colour change in a tropical python 
Biology Letters  2006;3(1):40-43.
Ontogenetic colour change is typically associated with changes in size, vulnerability or habitat, but assessment of its functional significance requires quantification of the colour signals from the receivers' perspective. The tropical python, Morelia viridis, is an ideal species to establish the functional significance of ontogenetic colour change. Neonates hatch either yellow or red and both the morphs change to green with age. Here, we show that colour change from red or yellow to green provides camouflage from visually oriented avian predators in the different habitats used by juveniles and adults. This reflects changes in foraging behaviour and vulnerability as individuals mature and provides a rare demonstration of the adaptive value of ontogenetic colour change.
doi:10.1098/rsbl.2006.0574
PMCID: PMC2373822  PMID: 17443961
colour polymorphism; ontogenetic colour change; crypsis; Morelia viridis; python
11.  Experience pays: offspring survival increases with female age 
Biology Letters  2006;3(1):44-46.
Life-history theory predicts that, in long-lived organisms, effort towards reproduction will increase with age, and research from oviparous vertebrates largely supports this prediction. In reptiles, where parental care occurs primarily via provisioning of the egg, older females tend to produce larger eggs, which in turn produce larger hatchlings that have increased survival. We conducted an experimental release study and report that maternal age positively influences offspring survivorship in the painted turtle (Chrysemys picta) and predicts offspring survival at least as well as hatchling body size does. These data suggest that, although increasing hatchling size is a major component of reproductive success in older individuals, other factors also contribute.
doi:10.1098/rsbl.2006.0573
PMCID: PMC2373821  PMID: 17443962
life-history theory; survivorship; body size; Chrysemys picta; turtle
12.  Continent-wide variation in feather colour of a migratory songbird in relation to body condition and moulting locality 
Biology Letters  2006;3(1):16-19.
Understanding the causes of variation in feather colour in free-living migratory birds has been challenging owing to our inability to track individuals during the moulting period when colours are acquired. Using stable-hydrogen isotopes to estimate moulting locality, we show that the carotenoid-based yellow–orange colour of American redstart (Setophaga ruticilla) tail feathers sampled on the wintering grounds in Central America and the Caribbean is related to the location where feathers were grown the previous season across North America. Males that moulted at southerly latitudes were more likely to grow yellowish feathers compared with males that moulted more orange–red feathers further north. Independent samples obtained on both the breeding and the wintering grounds showed that red chroma—an index of carotenoid content—was not related to the mean daily feather growth rate, suggesting that condition during moult did not influence feather colour. Thus, our results support the hypothesis that feather colour is influenced by ecological conditions at the locations where the birds moulted. We suggest that these colour signals may be influenced by geographical variation in diet related to the availability of carotenoids.
doi:10.1098/rsbl.2006.0572
PMCID: PMC2373820  PMID: 17443954
migration; carotenoids; stable isotopes; feather growth
13.  Positive short-term effects of sheep grazing on the alpine avifauna 
Biology Letters  2006;3(1):109-111.
Abstract
Grazing by large herbivores may negatively affect bird populations. This is of great conservation concern in areas with intensive sheep grazing. Sheep management varies substantially between regions, but no study has been performed in less intensively grazed systems. In a fully replicated, landscape scale experiment with three levels of sheep grazing, we tested whether the abundance and diversity of an assemblage of mountain birds were negatively affected by grazing or if grazing facilitated the bird assemblage. Density of birds was higher at high sheep density compared with low sheep density or no sheep by the fourth grazing season, while there was no clear effect on bird diversity. Thus, agricultural traditions and land use politics determining sheep density may change the density of avifauna in either positive or negative directions.
doi:10.1098/rsbl.2006.0571
PMCID: PMC2373819  PMID: 17443979
ecosystem function; livestock; biodiversity; birds; facilitation; trophic cascades
14.  Spatial genetic analysis and long-term mark–recapture data demonstrate male-biased dispersal in a snake 
Biology Letters  2006;3(1):33-35.
Dispersal is an important life-history trait, but it is notoriously difficult to study. The most powerful approach is to attack the problem with multiple independent sources of data. We integrated information from a 14-year demographic study with molecular data from five polymorphic microsatellite loci to test the prediction of male-biased dispersal in a common elapid species from eastern Australia, the small-eyed snake Rhinoplocephalus nigrescens. These snakes have a polygynous mating system in which males fight for access to females. Our demographic data demonstrate that males move farther than females (about twice as far on average, and about three times for maximum distances). This sex bias in adult dispersal was evident also in the genetic data, which showed a strong and significant genetic signature of male-biased dispersal. Together, the genetic and demographic data suggest that gene flow is largely mediated by males in this species.
doi:10.1098/rsbl.2006.0570
PMCID: PMC2373818  PMID: 17443959
sex-biased dispersal; mating system; movement patterns; spatial autocorrelation
15.  Feeding mechanics and bite force modelling of the skull of Dunkleosteus terrelli, an ancient apex predator 
Biology Letters  2006;3(1):76-79.
Placoderms are a diverse group of armoured fishes that dominated the aquatic ecosystems of the Devonian Period, 415–360 million years ago. The bladed jaws of predators such as Dunkleosteus suggest that these animals were the first vertebrates to use rapid mouth opening and a powerful bite to capture and fragment evasive prey items prior to ingestion. Here, we develop a biomechanical model of force and motion during feeding in Dunkleosteus terrelli that reveals a highly kinetic skull driven by a unique four-bar linkage mechanism. The linkage system has a high-speed transmission for jaw opening, producing a rapid expansion phase similar to modern fishes that use suction during prey capture. Jaw closing muscles power an extraordinarily strong bite, with an estimated maximal bite force of over 4400 N at the jaw tip and more than 5300 N at the rear dental plates, for a large individual (6 m in total length). This bite force capability is the greatest of all living or fossil fishes and is among the most powerful bites in animals.
doi:10.1098/rsbl.2006.0569
PMCID: PMC2373817  PMID: 17443970
placoderms; bite force; Dunkleosteus; biomechanics
16.  Eat now, pay later? Evidence of deferred food-processing costs in diving seals 
Biology Letters  2006;3(1):94-98.
Seals may delay costly physiological processes (e.g. digestion) that are incompatible with the physiological adjustments to diving until after periods of active foraging. We present unusual profiles of metabolic rate (MR) in grey seals measured during long-term simulation of foraging trips (4–5 days) that provide evidence for this. We measured extremely high MRs (up to almost seven times the baseline levels) and high heart rates during extended surface intervals, where the seals were motionless at the surface. These occurred most often during the night and occurred frequently many hours after the end of feeding bouts. The duration and amount of oxygen consumed above baseline levels during these events was correlated with the amount of food eaten, confirming that these metabolic peaks were related to the processing of food eaten during foraging periods earlier in the day. We suggest that these periods of high MR represent a payback of costs deferred during foraging.
doi:10.1098/rsbl.2006.0566
PMCID: PMC2373816  PMID: 17443975
diving; delayed digestion; seals; metabolic rate
17.  Conflict between direct and indirect benefits of female choice in desert Drosophila 
Biology Letters  2006;3(1):29-32.
Identifying the factors that contribute to the adaptive significance of mating preferences is one major goal of evolutionary research and is largely unresolved. Both direct and indirect benefits can contribute to mate choice evolution. Failure to consider the interaction between individual consequences of mate choice may obscure the opposing effects of individual costs and benefits. We investigate direct and indirect fitness effects of female choice in a desert fly (Drosophila mojavensis), a species where mating confers resistance to desiccation stress. Females prefer males that provide a direct benefit: greater resistance to desiccation stress. Mating preferences also appear to have indirect consequences: daughters of preferred males have lower reproductive success than daughters of unpreferred males, although additional experimentation will be needed to determine if the indirect consequences of female preferences actually arise from ‘sexually antagonistic’ variation. Nevertheless, the results are intriguing and are consistent with the hypothesis that an interaction between direct and indirect benefits maintains sexually antagonistic variation in these desert flies: increased desiccation resistance conferred by mating might offset the cost of producing low-fecundity daughters.
doi:10.1098/rsbl.2006.0565
PMCID: PMC2373815  PMID: 17443958
sexual selection; sexual antagonism; female mate choice; direct benefits; indirect benefits
18.  Harvesting of males delays female breeding in a socially monogamous mammal; the beaver 
Biology Letters  2006;3(1):106-108.
Human exploitation may skew adult sex ratios in vertebrate populations to the extent that males become limiting for normal reproduction. In polygynous ungulates, females delay breeding in heavily harvested populations, but effects are often fairly small. We would expect a stronger effect of male harvesting in species with a monogamous mating system, but no such study has been performed. We analysed the effect of harvesting males on the timing of reproduction in the obligate monogamous beaver (Castor fiber). We found a negative impact of harvesting of adult males on the timing of parturition in female beavers. The proportion of normal breeders sank from over 80%, when no males had been shot in the territories of pregnant females, to under 20%, when three males had been shot. Harvesting of males in monogamous mammals can apparently affect their normal reproductive cycle.
doi:10.1098/rsbl.2006.0563
PMCID: PMC2373813  PMID: 17443978
Castor fiber; life history; management; phenology; seasonality
19.  The nested structure of marine cleaning symbiosis: is it like flowers and bees? 
Biology Letters  2006;3(1):51-54.
In a given area, plant–animal mutualistic interactions form complex networks that often display nestedness, a particular type of asymmetry in interactions. Simple ecological and evolutionary factors have been hypothesized to lead to nested networks. Therefore, nestedness is expected to occur in other types of mutualisms as well. We tested the above prediction with the network structure of interactions in cleaning symbiosis at three reef assemblages. In this type of interaction, shrimps and fishes forage on ectoparasites and injured tissues from the body surface of fish species. Cleaning networks show strong patterns of nestedness. In fact, after controlling for species richness, cleaning networks are even more nested than plant–animal mutualisms. Our results support the notion that mutualisms evolve to a predictable community-level structure, be it in terrestrial or marine communities.
doi:10.1098/rsbl.2006.0562
PMCID: PMC2373812  PMID: 17443964
asymmetrical interactions; coevolutionary networks; coral reefs; null models
20.  Representational signalling in birds 
Biology Letters  2006;3(1):8-11.
Some animals give specific calls when they discover food or detect a particular type of predator. Companions respond with food-searching behaviour or by adopting appropriate escape responses. These signals thus seem to denote objects in the environment, but this specific mechanism has only been demonstrated for monkey alarm calls. We manipulated whether fowl (Gallus gallus) had recently found a small quantity of preferred food and then tested for a specific interaction between this event and their subsequent response to playback of food calls. In one treatment, food calls thus potentially provided information about the immediate environment, while in the other the putative message was redundant with individual experience. Food calls evoked substrate searching, but only if the hens had not recently discovered food. An identical manipulation had no effect on responses to an acoustically matched control call. These results show that chicken food calls are representational signals: they stimulate retrieval of information about a class of external events. This is the first such demonstration for any non-primate species. Representational signalling is hence more taxonomically widespread than has previously been thought, suggesting that it may be the product of common social factors, rather than an attribute of a particular phylogenetic lineage.
doi:10.1098/rsbl.2006.0561
PMCID: PMC2373811  PMID: 17443952
referential signalling; representational signalling; animal cognition; food calls
21.  Host plant and population determine the fitness costs of resistance to Bacillus thuringiensis 
Biology Letters  2006;3(1):82-85.
Novel adaptations often cause pleiotropic reductions in fitness. Under optimal conditions individual organisms may be able to compensate for, or reduce, these fitness costs. Declining environmental quality may therefore lead to larger costs. We investigated whether reduced plant quality would increase the fitness costs associated with resistance to Bacillus thuringiensis in two populations of the diamondback moth Plutella xylostella. We also measured the rate of decline in resistance on two host-plant (Brassica) species for one insect population (Karak). Population×plant species interactions determined the fitness costs in this study. Poor plant quality increased the fitness costs in terms of development time for both populations. However, fitness costs seen in larval survival did not always increase as plant quality declined. Both the fitness and the stability experiment indicated that fitness costs were higher on the most suitable plant for one population. Theoretically, if the fitness cost of a mutation interacts additively with environmental factors, the relative fitness of resistant insects will decrease with environmental quality. However, multiplicative costs do not necessarily increase with declining quality and may be harder to detect when fitness parameters are more subject to variation in poorer environments.
doi:10.1098/rsbl.2006.0560
PMCID: PMC2373810  PMID: 17443972
Bacillus thuringiensis; fitness cost; gene X environment interaction; tritrophic interaction; Plutella; Brassica
22.  The impact of climatic variation on the opportunity for sexual selection 
Biology Letters  2006;3(1):12-15.
Many studies have demonstrated influences of climatic variation on a variety of ecological processes, however, its impact on the potent evolutionary force of sexual selection has largely been ignored. The intensity of sexual selection is a fundamental parameter in animal populations, which depends upon the degree of polygamy and will probably be influenced by the impact of local climatic variation upon ‘environmental potential for polygamy’. Here, we provide evidence of a direct effect of local climatic variation on the intensity of sexual selection, by showing a clear correlation between local weather conditions and inter-annual changes in the degree of polygamy in a long-term study of colonially breeding grey seals (Halichoerus grypus). Our results show that changes in local weather conditions alter the annual proportion of males contributing to the effective population size (Ne) by up to 61%. Consequently, over the ‘lifetime’ of a cohort, a broader range of individuals will contribute genetically to the next generation if local weather conditions are variable. In the context of predicted future changes in climatic variation, these findings have broad implications for population genetics of socially structured animal systems through the major influence that the degree of polygamy has upon Ne.
doi:10.1098/rsbl.2006.0559
PMCID: PMC2373809  PMID: 17443953
climate; polygyny; reproductive success; effective population size; Halichoerus grypus
23.  The tail of the Ordovician fish Sacabambaspis 
Biology Letters  2006;3(1):72-75.
The tail of the earliest known articulated fully skeletonized vertebrate, the arandaspid Sacabambaspis from the Ordovician of Bolivia, is redescribed on the basis of further preparation of the only specimen in which it is most extensively preserved. The first, but soon discarded, reconstruction, which assumed the presence of a long horizontal notochordal lobe separating equal sized dorsal and ventral fin webs, appears to have considerable merit. Although the ventral web is significantly smaller than the dorsal one, the presence of a very long notochordal lobe bearing a small terminal web is confirmed. The discrepancy in the size of the ventral and dorsal webs rather suggests that the tail was hypocercal, a condition that would better accord with the caudal morphology of the living agnathans and the other jawless stem gnathostomes.
doi:10.1098/rsbl.2006.0557
PMCID: PMC2373808  PMID: 17443969
Vertebrata; Arandaspida; Ordovician; caudal fin
24.  Male swordtails court with an audience in mind 
Biology Letters  2006;3(1):5-7.
Females are usually considered to be the target of male courtship behaviour. In nature, however, social interactions rarely occur without other observers; thus, it is conceivable that some male courtship behaviours are directed not towards females, but rather towards male rivals. The northern swordtail, Xiphophorus birchmanni, is a freshwater fish found in high densities in natural streams. Males court by swimming close to and in parallel with the female, raising their large sail-like dorsal fin, and quivering briefly. Here, we show that females prefer males that display small dorsal fins to those with large ones, and that males are less aggressive to other males with large dorsal fins. Male swordtails also raise their dorsal fins more frequently when courting in the presence of other males. These results suggest that, despite female avoidance of large dorsal fins, males that raise their fin during courtship benefit by intimidating potential competitors; the intended receivers of this signal are thus males, not females. Intrasexual selection can therefore offset the forces of intersexual selection, even in a courtship display.
doi:10.1098/rsbl.2006.0556
PMCID: PMC2373807  PMID: 17443951
mate choice; competition; sexual selection; Poeciliidae

Results 1-25 (158)