Peter S. Harlow

Maternal Manipulation of Offspring Phenotypes via Nest‐Site Selection in an Oviparous Lizard

Mothers may be able to manipulate the phenotypes of their progeny not only via direct pathways (e.g., allocation of nutrients and energy), but also indirectly, by inducing particular developmental pathways through selection of nest sites and thus, incubation conditions. In the field, female skinks (Bassiana duperreyi) in montane southeastern Aus- tralia select nest sites with specific thermal characteristics-especially, a high mean tem- perature and a high diel range in temperature. Monitoring of 14 natural nests throughout most of the incubation period revealed considerable differences among nests in both means and variances of thermal regimes. Laboratory experiments on this species show that both the mean and the variance of incubation temperatures profoundly influence developmental rates (and hence, incubation periods) as well as the body shape, activity levels, thermo- regulatory behavior, and running speeds of the hatchlings. Hence, a females selection of a particular nest site can substantially modify both the time of emergence of the hatchlings, and the morphology and behavior of her offspring. Even within a single nest, minor dif- ferences among eggs in their depth below the ground surface will directly affect thermal variance, and so may strongly influence rates of embryogenesis and the phenotype of the hatchling. The effects of thermal variance (independent of the mean) on embryonic de- velopment rates and hatchling phenotypes suggest that data from constant-temperature incubation in the laboratory should be interpreted with caution.

THE INFLUENCE OF NEST TEMPERATURES AND MATERNAL BROODING ON HATCHLING PHENOTYPES IN WATER PYTHONS

Previous work on phenotypic plasticity in hatchling reptiles has dealt almost exclusively with lizards and turtles from temperate zone habitats, in taxa where the only maternal control over incubation regimes is exerted via nest site selection. In contrast, water pythons (Liasis fuscus) in northern Australia are tropical snakes that show facultative maternal brooding, with shivering thermogenesis to warm the clutch. Thus, incubation temperatures of this species are influenced both by nest site selection and by maternal care. We experimentally simulated three thermal regimes typical of different types of natural nests in our study population. These were (1) hot, stable temperatures typical of nests laid in the burrows of varanid lizards (constant 32°C); (2) lower and more variable temperatures typical of nests laid inside tree root boles, either with maternal attendance (diel range 27.1°–32.9°C); or (3) in root boles but without maternal attendance (24.3°–32.9°C). We incubated 187 eggs from 15 clutches obt...

Lingual salt glands inCrocodylus acutus andC. johnstoni and their absence fromAlligator mississipiensis andCaiman crocodilus

Summary1.Lingual salt glands, secreting hyperosmotic Na/K solutions in response to methacholine, are present inCrocodylus acutus andC. johnstoni but apparently absent from the alligatorids,Alligator mississipiensis andCaiman crocodilus.2.Both secretory rates (6–20 μmol/100 g·h) and concentrations (450–600 mM Na) of glandular secretions are essentially identical in the marine/estuarineC. acutus andC. porosus and significantly higher than in the freshwaterC. johnstoni (1–2 μmol/100 g·h; 320–420 mM Na).3.Lingual glands inAlligator secrete isosmotic Na/K at low rates (1–2 μmol/100 g·h) while those ofCaiman show no response to methacholine.4.The physiological contrast between alligatorids and crocodylids is reflected in distinct differences in the superficial appearance of the tongue and lingual pores.5.It is postulated that the alligatorid condition of low secretory capacity and isosmotic secretion reflects the primitive salivary function of lingual glands from which the salt-secreting capability in crocodylids was derived.

Shivering thermogenesis in a brooding diamond python, Python spilotes spilotes

, AND R. A. DANIELS. 1982. Distribution and ecology of stream fishes of the Sacramento-SanJoaquin drainage system, California. I. Fishes of the Pit River system, McCloud River system, and Surprise Valley region. Univ. Calif. Publ. Zool. 115. PIMENTEL, R. A. 1979. Morphometrics. The multivariate analysis of biological data. Kendall/Hunt Publishing Co., Dubuque. , AND D. S. FREY. 1978. Multivariate analysis of variance and discriminant analysis, p. 247-274. In: Quantitative ethology. P. W. Colgan (ed.). John Wiley, New York. ROBINS, C. R., AND R. R. MILLER. 1957. Classification, variation, and distribution of the sculpins, genus Cottus, inhabiting Pacific slope waters in California and southern Oregon, with a key to the species. Calif. Fish Game 43:213-233. RUTTER, C. 1908. The fishes of the Sacramento-San Joaquin basin, with a study of their distribution and variation. US Bur. Fish. Bull. 27:103-152. SNYDER, J. 0. 1917. The fishes of the Lahontan system of Nevada and northeastern California. Ibid. 35:31-86.

Susceptibility of amphibians to chytridiomycosis is associated with MHC class II conformation

The pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd) can cause precipitous population declines in its amphibian hosts. Responses of individuals to infection vary greatly with the capacity of their immune system to respond to the pathogen. We used a combination of comparative and experimental approaches to identify major histocompatibility complex class II (MHC-II) alleles encoding molecules that foster the survival of Bd-infected amphibians. We found that Bd-resistant amphibians across four continents share common amino acids in three binding pockets of the MHC-II antigen-binding groove. Moreover, strong signals of selection acting on these specific sites were evident among all species co-existing with the pathogen. In the laboratory, we experimentally inoculated Australian tree frogs with Bd to test how each binding pocket conformation influences disease resistance. Only the conformation of MHC-II pocket 9 of surviving subjects matched those of Bd-resistant species. This MHC-II conformation thus may determine amphibian resistance to Bd, although other MHC-II binding pockets also may contribute to resistance. Rescuing amphibian biodiversity will depend on our understanding of amphibian immune defence mechanisms against Bd. The identification of adaptive genetic markers for Bd resistance represents an important step forward towards that goal.

Reticulated pythons in sumatra : biology, harvesting and sustainability

Abstract Hundreds of thousands of giant snakes (Python reticulatus) are taken from the wild to be killed for their skins each year, raising doubts about the longterm sustainability of this offtake. We visited four locations in northern Sumatra (Medan, Seisuka, Rantauprapat and Cikampak) at four times of year and gathered information on the sizes, sexes, reproductive status and food habits of 784 slaughtered pythons. Pythons in northern Sumatra mature at larger body sizes than do those studied previously in southern Sumatra (Palembang). Their seasonal timing of reproduction is shifted appreciably, presumably because the two areas lie on opposite sides of the equator. The slaughtered animals are mainly adult males and adult plus juvenile females. Females attain larger sizes than males, but very large females are rarely captured. This bias may reflect size-related shifts in habitat selection; smaller snakes (including adult males of all sizes, and recently-matured females) feed primarily on commensal rats and hence are abundant in disturbed (agricultural and village) habitats. Female pythons produce large clutches (mean=24.2) of large eggs (mass>250 g), but reproduce only once every 2 to 4 years. The apparent ability of reticulated python populations to withstand high levels of offtake may reflect their demography (rapid growth rates, early maturation, high fecundity), their flexibility in diets and habitat use, and their ability to evade detection (because neither foraging nor thermoregulation require extensive movements).

Life Underground: Food Habits and Reproductive Biology of Two Amphisbaenian Species from Southern Africa

Examination and dissection of 216 museum specimens of two species of amphisbaenians (the shovel-snouted Monopeltis anchietae and round-headed Zygaspis quadrifrons) from southern Africa provided data on morphology, sexual dimorphism, reproduction, and dietary habits. The two species differed considerably in absolute size, in body proportions (eg, head width relative to snout-vent length), and in the degree of sexual dimorphism in these traits. In the relatively heavy-bodied Monopeltis both sexes attained similar body lengths, but females had wider heads than conspecific males. Conversely, in the thin-bodied Zygaspis, females attained larger body sizes than conspecific males, and there was no sexual dimorphism in head size. Clutch sizes were small in both species (means of 2.4 neonates in Monapeltis, 3.3 eggs in Zygaspis) and were not correlated with maternal body size. Termites were the most common prey far both taxa, but a wide variety of other soft-bodied invertebrates (beetle larvae, caterpillars) was also consumed. The two species differed in dietary composition, mean prey size, and in the numbers of prey items per stomach. Stomachs of Monopeltis contained more prey items than stomachs of Zygaspis (means of 72.2 versus 13.0 prey items) and prey ingested by Monopeltis were larger than those of Zygaspis. In Monopeltis, there was a significant positive correlation between predator size and prey number, but larger lizards continued to feed on relatively small prey. The reverse pattern was found in Zygaspis. The substantial differences in trophic biology between these two taxa and other sympatric fossorial reptiles, suggest that adaptations to fossoriality do not constrain ecological diversity within burrowing squamates.

Prior infection does not improve survival against the amphibian disease chytridiomycosis

Many amphibians have declined globally due to introduction of the pathogenic fungus Batrachochytrium dendrobatidis (Bd). Hundreds of species, many in well-protected habitats, remain as small populations at risk of extinction. Currently the only proven conservation strategy is to maintain species in captivity to be reintroduced at a later date. However, methods to abate the disease in the wild are urgently needed so that reintroduced and wild animals can survive in the presence of Bd. Vaccination has been widely suggested as a potential strategy to improve survival. We used captive-bred offspring of critically endangered booroolong frogs (Litoria booroolongensis) to test if vaccination in the form of prior infection improves survival following re exposure. We infected frogs with a local Bd isolate, cleared infection after 30 days (d) using itraconazole just prior to the onset of clinical signs, and then re-exposed animals to Bd at 110 d. We found prior exposure had no effect on survival or infection intensities, clearly showing that real infections do not stimulate a protective adaptive immune response in this species. This result supports recent studies suggesting Bd may evade or suppress host immune functions. Our results suggest vaccination is unlikely to be useful in mitigating chytridiomycosis. However, survival of some individuals from all experimental groups indicates existence of protective innate immunity. Understanding and promoting this innate resistance holds potential for enabling species recovery.

Reproductive Biology and Food Habits of Horned Adders, Bitis caudalis (Viperidae), from Southern Africa

Horned adders (Bitis caudalis) are small heavy-bodied viperid snakes widely distributed across a range of habitat types in southern Africa. Measurement and dissection of 580 preserved specimens in museum collections provided information on morphology, food habits, and reproductive biology of this species. In particular, it enabled us to assess the effects of sex and habitat type (arid to mesic) on adult body sizes and shapes, dietary composition, and reproductive output. Female horned adders mature at larger sizes than do males and grow much larger. At the same snout-vent length, females have larger heads and shorter tails than do males. Arid-zone snakes are longer and thinner than conspecifics from more mesic areas and have longer tails and larger heads. Horned adders feed primarily on lizards (especially lacertids, skinks, and geckos) but also take other small vertebrates. Dietary composition varies according to the snakes body size, sex, and geographic location: endothermic prey are taken mostly by larger snakes; by females rather than males; and by arid-zone rather than mesic-habitat snakes. Most prey are small relative to predator size, especially in large snakes. Litter sizes (3-19 offspring) increase with maternal body size, with no significant geographic differences in this relationship. However, reproductive frequency (as inferred from the proportion of adult females that were reproductive when collected) was significantly higher in mesichabitat snakes (> 50%) than in their arid-zone relatives (15%). Habitat-associated differences in resource availability may have affected traits such as body size and shape, degree of dietary specialization, growth rates and female reproductive frequencies.

Conflicts between Courtship and Thermoregulation: The Thermal Ecology of Amorous Male Garter Snakes (Thamnophis sirtalis parietalis, Colubridae)

Thermoregulatory behavior is an important component of daily activities for many reptiles, especially for small heliothermic (sun‐basking) species that inhabit cold climates. However, the relative costs and benefits of thermoregulation depend on numerous factors, such that reptiles may sometimes accord a low priority to precise control of body temperatures. We observed and radio tracked garter snakes (Thamnophis sirtalis parietalis) in central Manitoba during the mating season (spring). Previous studies on this species have documented precise behavioral regulation of body temperatures during summer. In contrast, the courting snakes that we studied in springtime spent little time in overt thermoregulatory behavior. Body temperatures were extremely variable (both in outdoor enclosures and in the field) despite abundant opportunities for more precise thermal control. These small elongate reptiles cool so quickly (relative to the time periods needed for effective courtship) that any benefit to higher body temperatures would be transitory at best. Experiments show that hotter males are no better at obtaining matings or at detecting predators. Thus, male garter snakes concentrate on courtship rather than on basking. In the face of conflicting priorities, reptiles may often forgo precise thermoregulation because its benefits are too low, and its costs too high, compared with alternative behaviors.