Past Reptile Research
The small island of Shedao in north-eastern China lies on a major migratory pathway for small birds. It is also home to an extraordinarily dense population of pit-vipers (Gloydius shedaoensis, pictured) that feed on the birds during their brief migratory periods in spring and autumn. The snakes are inactive the rest of the year. Together with Sun Li-xin, Rick has visited Shedao to study the biology of this remarkable population. We have initiated radiotelemetry and mark-recapture studies, and conducted simple field experiments to clarify cues for prey selection and habitat use by free-ranging snakes.
Rick has collaborated with Xavier Bonnet and his colleagues to examine the ways in which female aspic vipers (Vipera aspis, pictured) allocate energy to reproduction. These studies involve examining the relationships between energy acquisition, "costs of reproduction", and packaging of energy in the trade-off between offspring size and offspring number.
In many reptile species, an individual's sex is determined not by its genes, but by the incubation temperatures that it experiences as an embryo. Our recent work has shown that both processes can interact to modify offspring sex; that is, sex chromosomes can be over-ridden by low-temperature incubation. This topic is a central focus of current research by Dan Warner who is investigating TSD in jacky lizards (Amphibolurus muricatus, pictured). Raju Radder is also focussing his research in this area, mostly on montane scincid lizards with complex multifactorial sex determination.
Biologists traditionally have viewed mating systems in terms of cooperation between males and females to achieve reproductive success. However, recent studies suggest that there may be a substantial "conflict of interest" between the sexes. For example, male garter snakes (Thamnophis sirtalis parietalis, below) obtain matings forcibly, by inducing hypoxic stress in females - even though courtship in this species superficially appears very gentle and ritualised. We are also exploring sexual conflict in cane toads, with a view to intensify this conflict to control toad populations.
Life-history theory suggests that a major evolutionary determinant of reproductive effort should be the associated "costs" - that is, how much does an extra investment in reproduction (e.g., more or larger babies) reduce a female's probability of surviving to reproduce again in the following season? We are conducting experimental studies to manipulate reproductive expenditure and examine the consequences of such changes.
Juveniles of some venomous snake species look remarkably like non-venomous snakes living in the same area. For example, juvenile cottonmouth mocassins (Agkistrodon piscivorus, pictured) look just like watersnakes (Nerodia sp.), especially to elderly herpetologists with diminishing visual acuity. Rick Shine has recently conducted a simple manipulative experiment to evaluate the consequences of this mimicry system, using himself as the subject.
Photographs © R. Shine, P. Harlow, D. O'Connor, G. Barrott-Brown, S. Shetty, M. Elphick, P. Laboute, D. Warner, J. Webb and C. Masters