Reproducing lizards modify sex allocation in response to operational sex ratios

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

Reproductive modes in lizards: measuring fitness consequences of the duration of uterine retention of eggs

1. One of the primary axes of life-history variation involves the proportion of embryonic development for which the offspring is retained within its parent's body; understanding trade-offs associated with prolonging that period thus is a critical challenge for evolutionary ecology.\ud \ud 2. Prior to oviposition, most oviparous squamate reptiles retain developing eggs in utero for about one-third of embryogenesis; the strong conservatism in this trait is a major puzzle in reptilian reproduction. To clarify fitness consequences of this prolonged uterine retention, we need to experimentally modify the trait and examine the effects of our manipulation.\ud \ud 3. We used transdermal application of corticosterone to induce gravid scincid lizards (Bassiana duperreyi) to lay their eggs 'prematurely', with relatively undeveloped embryos. Corticosterone application induced females to oviposit sooner (mean of 5.41 ± 0.51 days post-treatment) at earlier embryonic developmental stage (27 ± 0.21) than did controls (13.2 ± 1.22 days; embryonic stage 30.4 ± 0.16).\ud \ud 4. Corticosterone levels in the egg yolk were unaffected by maternal treatment, so effects of earlier oviposition should not be confounded by endocrine disruption of embryogenesis. Nonetheless, early oviposition reduced hatchling fitness. Hatching success was lower, incubation periods post-laying were increased, and neonates from eggs laid at earlier embryonic stages were smaller and slower.\ud \ud 5. These results suggest that retention of developing eggs in utero by oviparous squamates enhances maternal fitness, and does so via modifications to offspring phenotypes rather than (for example) due to accelerated developmental rates of eggs in utero compared to in the nest.\ud \ud 6. More generally, our data support optimality models that interpret interspecific variation in the duration of maternal–offspring contact in terms of the selective forces that result from earlier vs. later termination of that maternal investment

Chytrid infection and post-release fitness in the reintroduction of an endangered alpine tree frog

Global amphibian decline and extinction has been associated with the spread of the pathogenic chytrid fungus (Batrachochytrium dendrobatidis, Bd). Despite extensive research, there have been no examples of effective management abating the ongoing impact of this pathogen in the wild. The endangered alpine tree frog (Litoria verreauxii alpina) has been extirpated from 80% of its former range because of Bd. We directly tested whether source population or host site influenced the efficacy of a reintroduction of L. v. alpina. We captive reared and released 1241 individuals from three different populations, two with a history of Bd exposure and one that was Bd-naïve, into two sites where they had historically occurred, and two sites where the species currently persists. Between 6 and 9 months post-release, we recaptured 4.83% of the released animals, and observed breeding at all sites. Both released and extant animals had similar susceptibility to infection; both groups increased in Bd infection prevalence and infection intensity throughout the breeding season. We did not detect any effect on survival by site of release; however, population of origin had a relatively large impact (ω = 0.454), and animals from one Bd-exposed population were recaptured significantly more than the animals from the other Bd-exposed population and the Bd-naive population. Population exposure history to the disease of reintroduced amphibians may be used to increase post-release fitness and conservation success. Selection for mechanisms of resistance should be further explored to help mitigate the impact of chytridiomycosis during reintroduction programmes

Consequences of maternal yolk testosterone for offspring development and survival : experimental test in a lizard

1. Hormone-mediated maternal effects and developmental plasticity are important sources of phenotypic variation, with potential consequences for trait evolution. Yet our understanding of the importance of maternal hormones for offspring fitness in natural populations is very limited, particularly in non-avian species.2. We experimentally elevated yolk testosterone by injection of a physiological dose into eggs of the lizard Ctenophorus fordi Storr, to investigate its roles in offspring development, growth and survival.3. Yolk testosterone did not influence incubation period, basic hatchling morphology or survival under natural conditions. However, there was evidence for increased growth in hatchlings from testosterone-treated eggs, suggesting that maternal hormones have potential fitness consequences in natural populations.4. The positive effect of prenatal testosterone exposure on postnatal growth could represent a taxonomically widespread developmental mechanism that has evolved into an adaptive maternal effect in some taxa, but remains deleterious or selectively neutral in others.5. A broader taxonomic perspective should increase our understanding of the role of physiological constraints in the evolution of endocrine maternal effects.<br /

The decline of the endemic Fijian crested iguana Brachylophus vitiensis in the Yasawa and Mamanuca archipelagos, western Fiji

The endemic Fijian crested iguana Brachylophus vitiensis, categorized as Critically Endangered on the IUCN Red List, has been recorded from several islands in western Fiji. We conducted a survey for the crested iguana on 12 uninhabited and five inhabited islands in the Yasawa and Mamanuca archipelagos of western Fiji in September 2000. Night searches for sleeping iguanas along a total of 11.2 km of forest transects suggest that crested iguanas are either extremely rare or extinct on all of these islands. Although we collectively searched a total of 44 km of transect over 123 person hours, we located crested iguanas on only four islands: three small uninhabited islands (all, 73 ha) and one large inhabited island (22 km). In July 2003 we resurveyed two islands identified as having the best potential for the long-term conservation of crested iguanas, and found that populations were continuing to decline. We suggest that the scarcity of crested iguanas on all islands surveyed is due to the combination of habitat loss and the introduction of exotic predators. All islands surveyed have free ranging goats, forest fires have occurred repeatedly over the last few decades, and feral cats are established on many islands. To reverse the population decline of this species immediate intervention is required on selected islands to halt continuing forest degradation and to clarify the effects of introduced predators

Genetic evidence for co-occurrence of chromosomal and thermal sex-determining systems in a lizard

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