Hatchling Traits Research Articles

4.P11. Clonal genotype plays an important role in determining hatchling traits in the face of diel incubation temperature variance in the parthenogenetic gecko (Heteronotia binoei)

4.P11. Clonal genotype plays an important role in determining hatchling traits in the face of diel incubation temperature variance in the parthenogenetic gecko (Heteronotia binoei)

Are the phenotypic traits of hatchling lizards affected by maternal allocation of steroid hormones to the egg?

In lizards as in many other kinds of animals, strong maternal effects on the phenotypic traits of hatchlings are frequently reported. One plausible non-genetic mechanism that might produce such differences among clutches involves maternal allocation of steroid hormones. Lizard eggs often display considerable inter-clutch variation in the quantities of maternally allocated steroids, and exogenous application of such steroids has been reported to influence the phenotypic traits (especially, sex) of hatchlings. We examined correlations between naturally occurring yolk steroid levels and offspring traits in the scincid lizard Bassiana duperreyi, and also conducted experimental trials (exogenous application of testosterone or 17β-oestradiol to eggs) to test for causal effects of hormones. Although exogenous hormones readily reversed sex of the hatchling lizards, no other phenotypic traits of the hatchlings (morphology, locomotor performance) were significantly correlated with naturally occurring levels of testosterone, dihydrotestosterone or estrogen, nor were these phenotypic traits significantly affected by exogenous application of hormones. Hence, our results do not support the hypothesis that reproducing female lizards manipulate the phenotypic traits of their offspring by differential allocation of steroid hormones.

The Influence of Incubation Temperature on Morphology, Locomotor Performance, and Cold Tolerance of Hatchling Chinese Three-Keeled Pond Turtles, Chinemys reevesii

ABSTRACT We incubated eggs of the Chinese three-keeled pond turtle (Chinemys reevesii) at 4 constant temperatures to assess the influence of these thermal regimes on incubation length, hatching success, and phenotypic traits of hatchlings. Eggs incubated at 24° and 27°C produced larger hatchlings in body mass, carapace size, and limb length than did those from 30° and 33°C. Hatchlings from 27° and 30°C crawled and swam faster than did their counterparts from 24° and 33°C. The critical thermal minima of hatchlings incubated at 30° and 33°C were higher than those of hatchlings from 24° and 27°C.

Phenotypic plasticity in reproductive traits induced by food availability in a lacertid lizard, Takydromus septentrionalis

Understanding the proximate determinants of phenotypic variations in life‐history traits can provide powerful insights into a species’ life‐history strategies. I experimentally manipulated availability of food (high vs low) to examine plasticity in the reproductive traits of northern grass lizards, Takydromus septentrionalis (Lacertidae), from eastern China. Food availability significantly affected reproductive frequency and thereby seasonal reproductive output, but had little effect on reproductive output per clutch. Low‐food females postponed reproduction and produced less clutches in the reproductive season than did high‐food females. After producing their second clutches, low‐food females were in lower body condition than the high‐food counterparts. By the end of the experiment, however, all females exhibited similar body condition. Clutch size and clutch mass differed between the first and second clutches but not between the treatments. Egg size and phenotypic traits of hatchlings (body size, morphology and locomotor performance) in T. septentrionalis did not vary significantly from first to second clutches nor between the two treatments. These results support optimal egg size (offspring) theory. Female T. septentrionalis “decide” whether or not to reproduce largely based on current energy intake; lowered feeding rates thus delay oviposition and reduce reproductive frequency. In contrast, clutch size, egg size and relative clutch mass remain unchanged.

Is increased maternal basking an adaptation or a pre-adaptation to viviparity in lizards?

Pregnant females modify their thermoregulatory behaviour in many species of viviparous (live-bearing) reptiles, typically maintaining higher and more stable body temperatures at this time. Such modifications often have been interpreted as adaptations to viviparity, functioning to accelerate embryonic development and/or modify phenotypic traits of hatchlings. An alternative possibility is that similar maternal thermophily may be widespread also in oviparous species and if so, would be a pre-adaptation (rather than an adaptation) to viviparity. Because eggs are retained in utero for a significant proportion of development even in oviparous reptiles, maternal thermophily might confer similar advantages in oviparous as in viviparous taxa. Experimental trials on montane oviparous scincid lizards (Bassiana duperreyi) support the pre-adaptation hypothesis. First, captive females (both reproductive and non-reproductive) selected higher temperatures than males. Second, experimentally imposing thermal regimes on pregnant females significantly affected their oviposition dates and the phenotypic traits (body shape, running speed) of their hatchlings. Thus, as for many other behavioural correlates of pregnancy in viviparous reptiles, maternal thermophily likely may have already been present in the ancestral oviparous taxa that gave rise to present-day viviparous forms.

Do Changing Moisture Levels during Incubation Influence Phenotypic Traits of Hatchling Snakes (Tropidonophis mairii, Colubridae)?

Phenotypic traits (e.g., size, strength, speed) of hatchlings in many reptile species are influenced by hydric conditions in the nest. Previous experiments have focused on comparisons between eggs maintained under constant (but different) conditions, but eggs in natural nests frequently experience strong temporal shifts in soil water content during incubation. Keelback snakes (Tropidonophis mairii) in the Australian wet-dry tropics nest over most of the year, so early nests experience decreasing water availability during development, late nests experience increases, and others (midyear) remain stable in this respect. We mimicked these three conditions and incubated 54 eggs (nine from each of six clutches) in a split-clutch design to maintain the same average water content but with differing trajectories through incubation. The experimental treatments significantly affected the total amount of water taken up by the eggs (and thus final egg mass), but incubation periods were unaffected. Hatchling size but not strength showed minor but statistically significant effects of incubation regimes. The ability of keelback eggs to take up excess water whenever it becomes available (either early or late in development) and to retain it even when conditions change buffers embryogenesis effectively (but not completely) against fluctuations in soil water conditions.

The influence of maternal thermal environments on reproductive traits and hatchling traits in a Lacertid lizard, Takydromus septentrionalis

The thermal environment can induce substantial variation in important life-history traits. Experimental manipulation of the thermal environment can help researchers determine the contribution of this factor to phenotypic variation in life-history traits. During the reproductive season, we kept female northern grass lizards, Takydromus septentrionalis (Lacertidae), in three temperature-controlled rooms (25, 28 and 32 °C) to measure the effect of the maternal thermal environment on reproductive traits. Maternal thermal environment remarkably affected reproductive frequency and thereby seasonal reproductive output, but had little effect on reproductive traits per clutch or hatchling traits. Females kept at 32 °C produced more clutches and thus had shorter clutch intervals than females from 28 to 25 °C. Clutch size, clutch mass, relative clutch mass, egg size and hatchling traits did not vary among the three treatments. The eggs produced by the females were incubated at 27 °C and the traits of hatchlings were measured. The result that egg (offspring) size was independent of maternal thermal environments is consistent with the prediction of the optimal egg size (offspring) theory. The eggs produced by low temperature females (28 and 25 °C) took longer time to complete their post-oviposition development than did eggs produced by high temperature females (32 °C). This suggests that the eggs from low temperatures might have been laid when the embryos were at relatively early stages. Therefore, maternal thermal environment prior to oviposition could affect post-oviposition development in T. septentrionalis.

Effects of constant and fluctuating temperatures on egg survival and hatchling traits in the northern grass lizard (Takydromus septentrionalis, Lacertidae)

To understand how nest temperatures influence phenotypic traits of reptilian hatchlings, the effects of fluctuating temperature on hatchling traits must be known. Most investigations, however, have only considered the effects of constant temperatures. We incubated eggs of Takydromus septentrionalis (Lacertidae) at constant (24 degrees C, 27 degrees C, 30 degrees C and 33 degrees C) and fluctuating temperatures to determine the effects of these thermal regimes on incubation duration, hatching success and hatchling traits (morphology and locomotor performance). Hatching success at 24 degrees C and 27 degrees C was higher, and hatchlings derived from these two temperatures were larger and performed better than their counterparts from 30 degrees C and 33 degrees C. Eggs incubated at fluctuating temperatures exhibited surprisingly high hatching success and also produced large and well-performed hatchlings in spite of the extremely wide range of temperatures (11.6-36.2 degrees C) they experienced. This means that exposure of eggs to adversely low or high temperatures for short periods does not increase embryonic mortality. The variance of fluctuating temperatures affected hatchling morphology and locomotor performance more evidently than did the mean of the temperatures in this case. The head size and sprint speed of the hatchlings increased with increasing variances of fluctuating temperatures. These results suggest that thermal variances significantly affect embryonic development and phenotypic traits of hatchling reptiles and are therefore ecologically meaningful.

Genetic, prenatal, and postnatal correlates of dispersal in hatchling fence lizards (Sceloporus occidentalis)

Similarity of dispersal behavior among siblings is common in vertebrates. However, little is known about the factors (genetic, prenatal, postnatal) generating this similarity. Here we analyzed potential influences on the dispersal patterns of multiple families of hatchling fence lizards, Sceloporus occidentalis. We captured near-term females from the field, incubated their eggs in the laboratory, measured various traits of the hatchlings and dams, and then released the hatchlings at a number of sites in nature. We recaptured hatchlings 5–6 weeks later and measured the direct distance to the release site. Because we treated hatchlings (from eggs to release) randomly with respect to sibship, we eliminated the possibility that any observed sibling similarity in dispersal is merely an artifact of common postnatal influences. To analyze dispersal, we developed a new method that does not make an arbitrary choice of a threshold distance separating dispersers from nondispersers. We found a significant family effect on dispersal. We suspect that this family effect originates from genetic influences rather than from prenatal ones. Indeed, hatchling dispersal was remarkably unrelated to numerous traits (of clutches, mothers, or hatchlings) that might reflect prenatal effects. However, we did find that males were more likely to disperse than females, as predicted for polygynous species. Finally, characteristics of the release site did not appear to influence dispersal.

Effects of Thermal and Hydric Environments on Incubating Eggs and Hatchling Traits in the Cobra, Naja naja atra

We examined in the laboratory the effects of thermal and hydric environments on incubating eggs and hatchling traits of Naja naja atra collected from a population near the northern distributional limit of the species in Zhejiang, eastern China. Eggs were incubated at temperatures of 24, 26, 30, and 32 ?C on substrates with water potentials of 0 and -220 kPa using a 4 x 2 factorial design. Temperature strongly affected hatching success, incubation length, water uptake by eggs during the course of incubation, and most morphological hatchling traits examined; it even affected embryonic mobilization of inorganic material from the shell. Hatching success was higher at 26 and 30?C but lower at 24 and 32?C. Eggs incubated at 26 and 30?C produced larger and heavier hatchlings that also contained more inorganic material and energy than did eggs incubated at lower and higher temperatures. Hatchlings from eggs incubated at 24 and 32?C were similar in size and mass, but hatchlings from eggs incubated at 32?C had larger residual yolks. De- formed hatchlings were found at 24, 30, and 32?C, the frequency being independent of incubation temper- ature. At the time of hatching, shells from eggs incubated at 24?C had greater dry mass and contained more ash, suggesting that less inorganic material was withdrawn from the shell by embryos developing at 24?C. Compared with temperature, water potential was not an important source of variation for the hatchling traits we examined, although it did influence water uptake by eggs during incubation and hatching success at 24?C. The effects of temperature were independent of the effects of water potential. Variation in size and mass induced by incubation temperature may be important to posthatching survival and fitness of hatch- lings.

The effect of short-term weather fluctuations on temperatures inside lizard nests, and on the phenotypic traits of hatchling lizard

Can short-term stochastic variation in local weather conditions modify the thermal conditions inside lizard nests, and thus (potentially) the developmental rates, hatching success, and phenotypic traits of hatchlings from these nests? This hypothesis requires that (i) natural nests are poorly buffered thermally, such that ambient regimes affect temperatures inside the nest, and (ii) short-term thermal variations modify attributes of the offspring. Field data on natural nests of the sub-alpine skink Bassiana duperreyi confirm the existence of this first effect, and laboratory experiments substantiate the latter. Exposure to warmer-than-usual temperatures for 2 weeks during the 9- to 16-week incubation period doubled hatching success, and significantly modified hatchling phenotypes (hatching dates, offspring size and locomotor performance). The proportion of development completed prior to this exposure influenced the degree of response. Exposure to a brief «window» of higher-than-usual temperatures soon after oviposition had more effect on hatching time, egg survival and hatchling phenotypes than if the exposure occurred later in development. Thus, minor variations in weather conditions during incubation may have substantial effects on reptile populations.

The effect of short-term weather fluctuations on temperatures inside lizard nests, and on the phenotypic traits of hatchling lizards

Abstract Can short-term stochastic variation in local weather conditions modify the thermal conditions inside lizard nests, and thus (potentially) the developmental rates, hatching success, and phenotypic traits of hatchlings from these nests? This hypothesis requires that (i) natural nests are poorly buffered thermally, such that ambient regimes affect temperatures inside the nest, and (ii) short-term thermal variations modify attributes of the offspring. Field data on natural nests of the sub-alpine skink Bassiana duperreyi confirm the existence of this first effect, and laboratory experiments substantiate the latter. Exposure to warmer-than-usual temperatures for 2 weeks during the 9- to 16-week incubation period doubled hatching success, and significantly modified hatchling phenotypes (hatching dates, offspring size and locomotor performance). The proportion of development completed prior to this exposure influenced the degree of response. Exposure to a brief «window» of higher-than-usual temperatures soon after oviposition had more effect on hatching time, egg survival and hatchling phenotypes than if the exposure occurred later in development. Thus, minor variations in weather conditions during incubation may have substantial effects on reptile populations.

Delayed Hatching of Salamander Eggs in Response to Enhanced Larval Predation Risk

To our knowledge, this article presents the first test of the hypothesis that variation in size-dependent predation risk on hatchings can cause adaptive shifts in the timing of egg hatching and thus on the size and developmental stage of new hatchlings. Earlier field experiments documented heavy predation by flatworms (Phagocotus gracilis) on smaller, less developed hatchling salamander larvae (Ambystoma texanum and Ambystoma barbouri) but little or no predation on larger, more developmentally advanced larvae. Here, we divided sibships into groups of 12 eggs and compared hatchling traits (time, size, and stage of hatching) for eggs reared in control fresh water versus water with flatworms, flatworm chemicals, or nonpredatory isopods. Both flatworms and flatworm chemicals induced eggs to delay their hatching to a later time and thus a larger size and more advanced developmental stage. In particular, sibships that tended to hatch early in control conditions delayed hatching in response to flatworms and flatworm chemicals, while sibships that hatched late in controls showed no response to either treatment. Nonpredatory isopods did not cause a significant change in hatching traits. Adaptive plasticity in hatching traits can provide excellent, unexploited opportunities for studying the evolution and ecological consequences of a life-history switch point.