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1.  Turtle embryos move to optimal thermal environments within the egg 
Biology Letters  2013;9(4):20130337.
A recent study demonstrated that the embryos of soft-shelled turtles can reposition themselves within their eggs to exploit locally warm conditions. In this paper, we ask whether turtle embryos actively seek out optimal thermal environments for their development, as do post-hatching individuals. Specifically, (i) do reptile embryos move away from dangerously high temperatures as well as towards warm temperatures? and (ii) is such embryonic movement due to active thermoregulation, or (more simply) to passive embryonic repositioning caused by local heat-induced changes in viscosity of fluids within the egg? Our experiments with an emydid turtle (Chinemys reevesii) show that embryos avoid dangerously high temperatures by moving to cooler regions of the egg. The repositioning of embryos is an active rather than passive process: live embryos move towards a heat source, whereas dead ones do not. Overall, our results suggest that behavioural thermoregulation by turtle embryos is genuinely analogous to the thermoregulatory behaviour exhibited by post-hatching ectotherms.
doi:10.1098/rsbl.2013.0337
PMCID: PMC3730644  PMID: 23760168
behavioural thermoregulation; ectotherm; embryo; oviparity
2.  Hotter nests produce smarter young lizards 
Biology Letters  2012;8(3):372-374.
A hatchling reptile's sex, body size and shape, and locomotor performance can be influenced not only by its genes, but also by the temperature that it experiences during incubation. Can incubation temperature also affect a hatchling's cognitive skills? In the scincid lizard Bassiana duperreyi, higher incubation temperatures enhanced the resultant hatchling's learning performance. Hence, factors such as maternal nest-site selection and climate change affect not only the size, shape and athletic abilities of hatchling reptiles, but also their ability to learn novel tasks.
doi:10.1098/rsbl.2011.1161
PMCID: PMC3367759  PMID: 22237502
incubation; temperature; learning; climate change
3.  Embryonic exposure to conspecific chemicals suppresses cane toad growth and survival 
Biology Letters  2011;8(2):226-229.
Adaptations to suppress the viability of conspecifics may provide novel ways to control invasive taxa. The spread of cane toads (Rhinella marina) through tropical Australia has had severe ecological impacts, stimulating a search for biocontrol. Our experiments show that cane toad tadpoles produce waterborne chemical cues that suppress the viability of conspecifics encountering those cues during embryonic development. Brief (72 h) exposure to these cues in the egg and post-hatching phases massively reduced rates of survival and growth of larvae. Body sizes at metamorphosis (about three weeks later) were almost twice as great in control larvae as in tadpole-exposed larvae. The waterborne cue responsible for these effects might provide a weapon to reduce toad recruitment within the species' invaded range.
doi:10.1098/rsbl.2011.0794
PMCID: PMC3297388  PMID: 21880623
alien species; Anura; Bufo marinus; competition; larva; pheromonal communication
4.  Geographic variation in the age of temperate-zone reptile and amphibian species: Southern Hemisphere species are older 
Biology Letters  2010;7(1):96-97.
Despite controversy over alternative definitions, the species is the fundamental operational unit of biodiversity, and species are the building-blocks of conservation. But is a ‘species’ from one part of the world the same as a ‘species’ from elsewhere? Our meta-analysis of molecular phylogenetic data reveals that reptile and amphibian species distributed in temperate-zone areas of the Northern Hemisphere are younger than taxa from the Southern Hemisphere, probably reflecting the greater impact of past climatic variation on Northern Hemisphere habitats. Because a species' age may influence its vulnerability to anthropogenic threats, geographical variation in species ages should be incorporated into conservation planning.
doi:10.1098/rsbl.2010.0557
PMCID: PMC3030887  PMID: 20659925
reptile; amphibian; molecular dating; intraspecific diversification; conservation status
5.  Turgid female toads give males the slip: a new mechanism of female mate choice in the Anura 
Biology Letters  2010;6(3):322-324.
In many anuran species, males vocalize to attract females but will grasp any female that comes within reach and retain their hold unless displaced by a rival male. Thus, female anurans may face strong selection to repel unwanted suitors, but no mechanism is known for doing so. We suggest that a defensive trait (the ability to inflate the body to ward off attack) has been co-opted for this role: by inflating their bodies, females are more difficult for males to grasp and hence, it is easier for another male to displace an already amplexed rival. Inflating a model female cane toad (Bufo marinus) strongly reduced a male's ability to maintain amplexus; and females who were experimentally prevented from inflating their bodies experienced no successful takeovers from rival males, in contrast to control females. Thus, the ability of a female cane toad to inflate her body may allow her to manipulate the outcome of male–male competition. This overlooked mechanism of anuran mate choice may reflect a common evolutionary pattern, whereby females co-opt defensive traits for use in sexual selection.
doi:10.1098/rsbl.2009.0938
PMCID: PMC2880058  PMID: 20053661
Amphibia; anti-predator; co-optation; male–male rivalry; sexual selection
6.  Kleptothermy: an additional category of thermoregulation, and a possible example in sea kraits (Laticauda laticaudata, Serpentes) 
Biology Letters  2009;5(6):729-731.
Lacking the capacity for thermogenesis, most ectotherms inhabiting thermally heterogeneous environments rely instead upon exploiting that ambient heterogeneity. In many cases they maintain body temperatures within a narrow range despite massive spatial and temporal variation in ambient conditions. Reliance on diverse thermal opportunities is reflected in specific terms for organisms that bask in sunlight to regulate their temperature (heliotherms), or that press their bodies against warm substrates to facilitate heat flow (thigmotherms), or that rely on large body mass to maintain thermal constancy (gigantothermy). We propose an additional category of thermoregulators: kleptotherms, which regulate their own temperature by ‘stealing’ heat from other organisms. This concept involves two major conditions: the thermal heterogeneity created by the presence of a warm organism in a cool environment and the selective use of that heterogeneity by another animal to maintain body temperatures at higher (and more stable) levels than would be possible elsewhere in the local area. Kleptothermy occurs in endotherms also, but is usually reciprocal (rather than unilateral as in ectotherms). Thermal monitoring on a small tropical island documents a possible example of kleptothermy, based on high stable temperatures of a sea snake (Laticauda laticaudata) inside a burrow occupied by seabirds.
doi:10.1098/rsbl.2009.0550
PMCID: PMC2828009  PMID: 19656862
ectothermy; thermoregulation; thigmothermy; reptile; snake
7.  Genetic evidence for co-occurrence of chromosomal and thermal sex-determining systems in a lizard 
Biology Letters  2007;4(2):176-178.
An individual's sex depends upon its genes (genotypic sex determination or GSD) in birds and mammals, but reptiles are more complex: some species have GSD whereas in others, nest temperatures determine offspring sex (temperature-dependent sex determination). Previous studies suggested that montane scincid lizards (Bassiana duperreyi, Scincidae) possess both of these systems simultaneously: offspring sex is determined by heteromorphic sex chromosomes (XX–XY system) in most natural nests, but sex ratio shifts suggest that temperatures override chromosomal sex in cool nests to generate phenotypically male offspring even from XX eggs. We now provide direct evidence that incubation temperatures can sex-reverse genotypically female offspring, using a DNA sex marker. Application of exogenous hormone to eggs also can sex-reverse offspring (oestradiol application produces XY as well as XX females). In conjunction with recent work on a distantly related lizard taxon, our study challenges the notion of a fundamental dichotomy between genetic and thermally determined sex determination, and hence the validity of current classification schemes for sex-determining systems in reptiles.
doi:10.1098/rsbl.2007.0583
PMCID: PMC2429925  PMID: 18089519
discordant sex; reptile; sex chromosomes; temperature-dependent sex determination
8.  Like mother, like daughter: inheritance of nest-site location in snakes 
Biology Letters  2007;3(2):131-133.
A trait can be passed from parents to offspring even if it has no genetic basis. For example, if daughters return to reproduce at the same sites where they were hatched themselves, nest-site location is consistent within matrilineages. Most cases of natal homing (nest-site philopatry) across generations have been inferred from molecular evidence rather than directly demonstrated, and involve species with low dispersal abilities. However, some animals disperse long distances but then return to their own place of birth to reproduce, based on cues imprinted early in their own development. Our field studies on tropical natricine snakes (Tropidonophis mairii, Colubridae) show that when they are ready to nest, females return to the sites where their mothers were captured pre-nesting, and where they themselves were released as hatchlings.
doi:10.1098/rsbl.2006.0605
PMCID: PMC2375938  PMID: 17284402
heritability; nesting; philopatry; reptile
9.  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
10.  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
11.  Thermally induced torpor in fullterm lizard embryos synchronizes hatching with ambient conditions 
Biology Letters  2006;2(3):415-416.
Eggs inside an underground nest have limited access to information about above-ground conditions that might affect the survival of emerging hatchlings. Our measurements of heart rates of embryos inside the intact eggs of montane lizards (Bassiana duperreyi, Scincidae) show that low temperatures induce torpor in fullterm embryos, but do not do so during earlier embryogenesis or later, post-hatching. Because above-ground conditions affect soil temperatures, this stage-dependent torpor effectively restricts hatching to periods of high ambient temperatures above ground. Torpor thus can function not only to synchronize activity with suitable environmental conditions during post-hatching life (as reported for many species), but also can occur in embryos, to synchronize hatching with above-ground conditions that facilitate successful emergence from the nest.
doi:10.1098/rsbl.2006.0495
PMCID: PMC1686188  PMID: 17148418
embryogenesis; metabolic rate; heart rate; reptile
12.  Does body volume constrain reproductive output in lizards? 
Biology Letters  2005;1(1):98-100.
The numbers and sizes of eggs produced by adult females ultimately determine the viability of populations, as well as the evolutionary fitness of the females themselves. Despite an enormous amount of literature on the adaptive significance of fecundity variation within and among populations, simpler questions—such as the proximate mechanisms by which a female determines her clutch size—have attracted less attention. Our surgical manipulations show that the amount of space available to hold eggs within a female's abdomen influences her total reproductive allocation, enabling her to flexibly modify her reproductive output as she grows larger.
doi:10.1098/rsbl.2004.0268
PMCID: PMC1629063  PMID: 17148138
clutch size; fecundity; life history; reptile

Results 1-12 (12)