Sexual Dimorphism of Digit-Length Ratio in a Viviparous Lizard: Influence of Age, but not Preservation State or Sex of Interuterine Twin.

The existence of sex differences in digit-length ratio (especially between the second and fourth digits, 2D:4D) is well established for humans from fetal life onwards, and has been linked with later performance. In rodents, the ratio is affected prenatally by exposure to androgens and estrogens, with some research suggesting an influence from sex of the neighbouring intrauterine fetus. However, the ubiquity and ontogenetic development of sexual dimorphism in digit ratios is not well established among wild amniotes. We report the first digit ratios for a gekkotan lizard, representing a speciose lineage in which viviparity has evolved independently from mammals and other reptiles. For the gecko Woodworthia "Otago/Southland", in which up to two embryos develop in separate uteri, we found: (1) significant sexual dimorphism in adults in 2D:3D of the right hindlimb only (larger in males), but not in 2D:4D for any limb; (2) no dimorphism in ratios for young juveniles, with no influence of sex of the interuterine twin, and no relationship with sprint speed; (3) in preserved tissues of the same juveniles, no sexual dimorphism in ratios, but a change in relative lengths of some digits with preservation. The ontogenetic pattern might be explained by altered sex-steroid exposure at the transition to adulthood rather than during prenatal development. Our results support a phylogenetic hypothesis that sauropsids (birds and reptiles) differ from mammals in the direction of sex difference, if present. Experiments are needed to establish the roles of androgens and estrogens in establishing these sex differences in lizards. Anat Rec, 301:1169-1178, 2018. © 2018 Wiley Periodicals, Inc.

Temperature selection by juvenile tuatara (Sphenodon punctatus) is not influenced by temperatures experienced as embryos.

Most reptiles thermoregulate to achieve body temperatures needed for biological processes, such as digestion and growth. Temperatures experienced during embryogenesis may also influence post-hatching growth rate, potentially through influencing post-hatching choice of temperatures. We investigated in laboratory settings whether embryonic temperatures (constant 18°C, 21°C and 22°C) influence selected body temperatures (Tsel) of juvenile tuatara (Sphenodon punctatus), providing a possible mechanism for differences in growth rates. We found that incubation temperature does not influence Tsel. Although the average daily mean Tsel was 21.6 ± 0.3°C, we recorded individual Tsel values up to 33.5°C in juvenile tuatara, which is higher than expected and above the panting threshold of 31-33°C reported for adults. We found diel patterns of Tsel of juvenile tuatara, observing a general pattern of two apparent peaks and troughs per day, with Tsel being significantly lower around dawn and at 1500h than any other time. When comparing our results with other studies on tuatara there is a remarkable consistency in mean Tsel of ~ 21°C across tuatara of different ages, sizes and acclimatization histories. The ability of juvenile tuatara to withstand a wide range of temperatures supports their former widespread distribution throughout New Zealand and warrants further investigation into their plasticity to withstand climate warming, particularly where they have choices of habitat and the ability to thermoregulate.

Maternal basking regime has complex implications for birthdate and offspring phenotype in a nocturnally foraging, viviparous gecko.

Maternal basking regime can affect gestation length in viviparous squamates, but effects on offspring phenotype in species with extended pregnancies and ability to delay the birth season are unclear. We investigated the effects of three maternal basking regimes on maternal thermoregulation, gestation length, pregnancy outcome and offspring phenotype in the gecko Woodworthia 'Otago/Southland'. This long-lived (30+ years), nocturnal forager has field pregnancies lasting up to 14 months, with fully developed offspring maintained in utero over winter. Within regimes, we also compared outcomes for spontaneous (early) deliveries with those from induced (late) deliveries to test the 'adaptive prolongation of pregnancy' hypothesis. Although a cool regime significantly extended gestation, the effect was reduced by increased maternal basking, and embryonic development under the cool regime was just as successful. Offspring from spontaneous births (but not induced births) were smaller and grew more slowly when from the cool regime. However, induced offspring did not differ in consistent ways from those delivered spontaneously and offspring from all groups had high viability, similar use of warm retreat sites and similar sprint speeds. Thus, consistent evidence for adaptive prolongation of pregnancy was lacking. Unusually for squamates, pregnant females can begin vitellogenesis before giving birth, and a profound drop in maternal body temperature near the end of pregnancy (∼6.3°C, confirmed under the warm regime) may assist survival of embryos in utero Female lizards that maintain fully developed embryos in utero have the potential to make complex trade-offs among birthdate, offspring phenotype and future reproduction.

Unusual change in activity pattern at cool temperature in a reptile (Sphenodon punctatus).

Animals that can be active both during day and night offer unique opportunities to identify factors that influence activity pattern. By experimental manipulations of temperatures under constant photoperiod, we aimed to determine if emergence, activity and thermoregulatory behaviour of juvenile tuatara (Sphenodon punctatus) varied at different temperatures (20°C, 12°C and 5°C). To help clarify its activity pattern, we compared tuatara with two lizard species endemic of the South Island of New Zealand for which activity pattern is known and clearly defined: the nocturnal common gecko Woodworthia "Otago/Southland" and the diurnal McCann׳s skink Oligosoma maccanni. Tuatara showed similar responses to both species of lizards. Similar to the diurnal skinks, tuatara emerged quickly at 20°C and 12°C while nocturnal geckos took more time to emerge. Like nocturnal geckos, tuatara continued to be active at 5°C, but only during the day. Interestingly, tuatara shifted from diurno-nocturnal activity at 20°C and 12°C to being strictly diurnal at 5°C. We suggest that this temperature-dependent strategy maximises their survival during cold periods.

Effects of early postnatal environment on phenotype and survival of a lizard.

Nutritional and thermal regimes experienced early in life can strongly influence offspring quality and ultimately adult life histories, especially in ectotherms. However, the importance of the interaction between diet and temperature during postnatal development and the effect on offspring quality are unknown. We compared offspring quality (size, shape, speed, behavior, and survival) of juvenile McCann's skinks (Oligosoma maccanni) housed outdoors under variable thermal conditions (under shelter, but exposed to daily and seasonal variations in light and temperature) with those housed indoors under more stable thermal conditions (controlled temperatures providing 30-40% more basking opportunity) and with a control group (open field conditions). For those caged in captivity (indoors and outdoors), we also compared outcomes between those fed a restricted diet and those fed ad libitum. By comparing individuals raised under different environmental regimes, we aimed to determine whether direct effects of temperature or indirect effects of food supply are more important for offspring quality. Individuals provided with food ad libitum grew faster, and attained larger sizes than those raised on a restricted diet or in the field. Activity rates were higher in individuals exposed to stable rather than variable thermal conditions. Survival post release in the field was highest for larger neonates, and lowest in individuals raised under stable thermal conditions and a restricted diet. We found little evidence for effects of an interaction between feeding and thermal regimes on most factors measured. However, the conditions experienced by young animals (especially diet) do influence important traits for population persistence, such as survival, and may influence key reproductive parameters (e.g., age and size at maturity), which could have implications for conservation management. Further research, including the ultimate influence of early environmental conditions on fecundity and life expectancy, is urgently needed.

Thermal dependence of locomotor performance in two cool-temperate lizards.

Temperate-zone ectotherms experience varying or very low ambient temperatures and may have difficulty in attaining preferred body temperatures. Thus, adaptations to reduce the thermal dependence of physiological processes may be present. We measured the optimal temperature range for sprint speed and compared it with the selected body temperatures (T (sel)) of two sympatric, cool-temperate lizards: the diurnal skink Oligosoma maccanni and the primarily nocturnal gecko Woodworthia (previously Hoplodactylus) "Otago/Southland". We also investigated whether time-of-day influenced sprint speed. Contrary to results for other reptiles, we found that time-of-day did not influence speed in either species. For each species, the optimal temperature range for sprinting and T (sel) overlapped, supporting the 'thermal coadaptation' hypothesis. However, the optimal range of temperatures for speed is not always attainable during activity by either species, which have limited opportunities to attain T (sel) in the field. The thermal sensitivity of sprint speed in these two species does not appear to have evolved to fully match their current thermal environment. More data on cold-adapted species are needed to fully understand physiological adaptation in ectotherms.

Does gestational temperature or prenatal sex ratio influence development of sexual dimorphism in a viviparous skink?

Prenatal sex ratio (through exposure to hormones from siblings in utero) can influence sexually dimorphic traits of many mammals; but research on viviparous reptiles has contrasting outcomes, which have yet to be resolved. The thermal environment experienced during gestation has a strong effect on the phenotype of reptiles, but whether this thermal effect overrides that of prenatal sex ratio has yet to be explored. We experimentally investigated whether the gestation temperature, or litter sex ratio, influences sexually dimorphic traits (head width and axilla-groin length) in a viviparous skink (Oligosoma maccanni). We found that gestation temperature had a significant influence on sexually dimorphic traits of neonates, and at 3 months of age still influenced head width. We found no evidence that traits in either sex were masculinized or feminized in response to litter sex ratio. The development of external sexual dimorphisms increased gradually (all thermal regimes pooled), with neonates showing no sexual dimorphism, 3-month-old juveniles showing some sexual dimorphism in head width, and adults having stronger, but incompletely separated, sexual dimorphism for both traits. We suggest that the overlap in sexually dimorphic traits of adult O. maccanni (and perhaps other reptiles) may be better explained by natural variation in temperatures experienced during embryonic development, rather than hormonal effects arising from litter sex ratio. The interaction of hormones and temperature during gestation and the effect of these factors on sexual dimorphism within reptiles deserve further exploration.

Nocturnal lizards from a cool-temperate environment have high metabolic rates at low temperatures.

Ectotherms from low-temperature environments have higher metabolic rates at low temperatures than those from warm-temperature environments. We predicted that nocturnal lizards, which are active at much lower environmental temperatures than diurnal lizards, would also have higher metabolic rates at low temperatures, and by association a lower thermal sensitivity (Q(10)) than diurnal and crepuscular lizards. We measured the rate of oxygen consumption (VO2) of eight cool-temperate species of lizard (four nocturnal, three diurnal, and one crepuscular) at 13 and 26°C and analyzed log transformations of these data using log mass as a covariate. As expected, VO2 was positively correlated with temperature in all eight species, with VO2 being two to four times higher at 26°C than at 13°C. As predicted, at 13°C (but not 26°C) the VO2 was significantly higher in nocturnal than diurnal lizards. Species-specific differences and mass scaling factors explain the patterns of thermal sensitivity seen among these eight lizard species. Thermal sensitivity is strongly influenced by mass, with smaller species generally having higher thermal sensitivity of their metabolic rate, and this result deserves further exploration among other ectotherms. We conclude that, along with the previously reported lower cost of locomotion found in nocturnal lizards, they also partially offset the thermal handicap of activity at low body temperatures by having an elevated VO2 at lower temperatures.

Incidence, causes and consequences of pregnancy failure in viviparous lizards: implications for research and conservation settings.

Research on the causes of pregnancy failure in vertebrates has historically been mammal-focussed. However, live-birth (viviparity) has evolved multiple times, and is present in all other vertebrate taxa except Aves and Agnatha. Viviparous lizards (O. Squamata, excluding snakes and amphisbaenians) provide a valuable experimental group when studying major evolutionary events and some are also species of high conservation value. Consequently, both researchers and herpetoculturists often require high reproductive output from captive-held lizards. We reviewed the literature to determine potential or known causes of pregnancy failure for captive lizards. Pregnancy success across species averages approximately 86%, but varies extensively and does not appear to be related to embryonic stage when brought into captivity or level of placentation. Causes of pregnancy failure also vary among species, but correct thermal environments are vital to success, and providing adequate nutrition before vitellogenesis increases the number of viable offspring. A coordinated sequence of hormonal changes involving both pro-pregnancy and pro-labour factors is important for successful pregnancies, although uncertainty remains around the maternal concentrations of corticosterone that allow successful development. Several research areas commonly studied in mammals have yet to be explored or fully addressed in pregnant lizards, including impacts of toxins, parasites, UV light and nutritional quality. As viviparity has evolved over 100 times in lizards, and many different levels of placentation exist, pregnant lizards provide valuable models for studies in ecology and evolution and offer a useful comparison for studies on other viviparous vertebrates.

Frequency of tail loss does not reflect innate predisposition in temperate New Zealand lizards.

Caudal autotomy (tail shedding) is a defence mechanism against predation which is used by lizards when other tactics, such as crypsis and escape, prove ineffective. The speed at which autotomy occurs has important implications for survival, and the accuracy of tail loss is of consequence for an individual's future fitness. Autotomy is shaped by both taxon-specific tail morphology as well as environmental factors such as predator history, and it can be difficult to distinguish between these processes. In this study, the frequency of tail-regeneration observed (field rate of autotomy), latency (speed of autotomy in the laboratory) and accuracy of tail loss were measured in six lizard species from two families (Scincidae and Diplodactylidae). The field rate and latency of autotomy was similar among all species except for the large nocturnal skink Oligosoma macgregori, which was less likely to autotomise. Latency and field rates of autotomy were not correlated, implying that the field rates of autotomy are related to predation attacks, social interactions, or some other environmental factor, rather than an innate disposition to autotomy. Further study, for example comparing populations with low and high predation pressure, will help to explain which of these factors are influencing autotomy rates.

Comparative phylogeography of three skink species (Oligosoma moco, O. smithi, O. suteri; Reptilia: Scincidae) in northeastern New Zealand.

Sea-level fluctuations during the Pliocene and Pleistocene have shaped the landscape of the Northland region of New Zealand. We examined the comparative phylogeography of three skink species (Oligosoma moco, O. smithi, O. suteri) in northeastern New Zealand in order to investigate the impact of the historical processes that have prevailed since the Pliocene on the Northland fauna. O. moco, O. smithi and O. suteri have similar distributions across northeastern New Zealand, frequently occurring in sympatry. We obtained sequence data from across the entire range of each species, targeting the ND2 mitochondrial gene. Using Neighbor-Joining, Maximum likelihood and Bayesian methods, our analysis revealed contrasting phylogeographic patterns in each species. We found substantial phylogeographic structure within O. moco, with three distinct clades identified. Similarly, deep phylogeographic divergence was evident within O. smithi, with three distinct clades present. Clade 1 included O. smithi populations from the Three Kings Islands and the western coastline of Northland, while Clade 2 encompassed the remainder of the range. However, since Clade 3 corresponded to a described species (O. microlepis), O. smithi might represent a species complex. In both O. moco and O. smithi, divergences among clades are estimated to have occurred in the Pliocene, with divergences within clades occurring during the Pleistocene. In contrast, genetic divergence among O. suteri populations was extremely limited and indicative of more recent divergences during the Pleistocene. The lack of phylogeographic structure in O. suteri might be a consequence of its oviparous reproductive mode, which restricted its distribution to warm northern refugia during glacial maxima. Differences in the ecology and biology of each species might have produced contrasting responses to the same historical processes, and ultimately diverse phylogeographic patterns. Our study reveals an absence of consistent and concordant phylogeographic patterns in the Northland biota, even within the same taxonomic group.

Daily patterns of metabolic rate among New Zealand lizards (Reptilia: Lacertilia: Diplodactylidae and Scincidae).

In addition to the effects of temperature fluctuations on metabolic rate, entrained endogenous rhythms in metabolism, which are independent of temperature fluctuations, may be important in overall energy metabolism in ectotherms. Daily entrained endogenous rhythms may serve as energy-conserving mechanisms during an animal's active or inactive phase. However, because nocturnal lizards often take advantage of thermal opportunities during the photophase (light), their daily metabolic rhythms may be less pronounced than those of diurnal species. We measured the rate of oxygen consumption (VO(2)) as an index of metabolic rate of eight temperate lizard species (four nocturnal, three diurnal, and one crepuscular/diurnal; n = 7-14) over 24 h at 13 degrees C and in constant darkness to test whether daily patterns (including amplitude, magnitude, and time of peak VO(2)) of metabolic rate in lizards differ with activity period. We also tested for phylogenetic differences in metabolic rate between skinks and geckos. Three daily patterns were evident: 24-h cycle, 12-h cycle, or no daily cycle. The skink Cyclodina aenea has a 12-h crepuscular pattern of oxygen consumption. In four other species, VO(2) increased with, or in anticipation of, the active part of the day, but three species had rhythms offset from their active phase. Although not correlated with activity period or phylogeny, amplitude of VO(2) may be correlated with whether a species is temperate or tropical. In conclusion, the metabolic rate of many species does not always correlate with the recorded activity period. The dichotomy of ecology and physiology may be clarified by more in-depth studies of species behaviors and activity periods.