Integrating the thermal physiologies of ectotherms and insular radiations:  Anolis lemurinus in the Cayos Cochinos and Bay Islands of Honduras

Although numerous studies have investigated the role of body size and prey partitioning in radiations of Anolis lizards, little attention has been given to the role of thermal biology in these speciation events.  Because all physiological functions operate within an optimal temperature range, and small ectotherms must behaviorally thermoregulate to maintain internal body temperatures within these ranges, it is reasonable to suppose that the way in which a given species exploits the available thermal landscape might dramatically affect its evolutionary trajectory.

In the near future, my research will integrate, in a spatially explicit way, the thermal biology of island dwelling Anolis lizards with the dynamics of community structure and insular radiation.

Broadly, I am intrigued by the potential for evolutionary trajectories to play out in a probabalistic manner.  Questions that have been steering my pursuit of this research area include:

1)  How much of what we see in nature (at the population and community level) is truly predictable, and how much is simply a relict of stochasticity and historical constraint? 

2)  How important is phylogenetic constraint on the thermal physiologies of ectotherms in determining their ability to successfully colonize and radiate throughout island archipelagos?

3)  How does the thermal optima of species in an island assemblage relate to the thermal optima of species from potential source populations?  In other words, in a given source population, are certain species more likely to colonize islands than others based on the evolution of their thermal preferences?

4)  Within an island assemblage, what role do thermal physiologies play in determining community structure?

5)  Within a lineage, how much of the variation in Anolis lizard thermoregulatory behavior can be accounted for by differences in the abiotic and biotic environments among islands, how much can be accounted for by lineage history, and how much can be accounted for by plasticity?

To get at these questions, I plan on examining species radiations within the context of thermoregulatory constraint on ancestral populations.  The Cayos Cochinos and Bay Islands of Honduras provide a great system for these kinds of questions, because most islands in this group have multiple populations of mainland-derived, and Caribbean-derived Anolis spp.  Moreover, the thermal landscapes of each island appear to differ from each other, and collectively they seem to differ quite a bit from the mainland. 

In addition to lineage-specific effects, this system provides the opportunity to look at the evolution of thermal optima and thermoregulatory behavior across a single radiation, that of A. lemurinus, which has populations on four of the islands that have been diverging in isolation for roughly 10,000 years.

The initial question that drove my thought process was this:  Why has A. lemurinus, and not some other polychrotid, been able to colonize a set of small islands occupied by sun-loving, Caribbean derived Anolis species?  This is a particularly surprising fact given that A. lemurinus, where it is found on the mainland, is an extreme shade-loving lizard found deep in primary forest.  One explanation might be that they are partitioning their thermal environment at the landscape level, and both clades are able to locate optimal thermal environments (with respect to their source populations) within each of the islands.  Nevertheless, because each of the Bay islands contain different polychrotid communities (including one island with only mainland derived species), and it is unlikely that the thermal characteristics of the hardwood forests of these islands mimic that of the mainland primary forests, this system provides an opportunity to observe the effects of phylogenetic constraint, thermal landcapes, and pressures from competitors on the evolution of thermal optima across a single species radiation.

This will be investigated in a spatially explicit way, for example, by developing detailed thermal profiles for each island in conjunction with operative temperature distributions for each polychrotid species present on each island.  The aforementioned, combined with field-active body temperatures and thermal preference ranges, would provide a window into how different populations of A. lemurinus are utilizing their thermal environment on each island in the archipelago (as well as how they are partitioning that environment with other, potentially competing, species of polychrotid lizard). 

In the very long term, by combining the above data types with thermal optima data for species from potential mainland (or island) species pools, I would like to develop this into theory about how phylogenetic constraint on thermal physiologies might affect the probability of certain species to colonize islands with differing thermal landscapes and species compositions, and how this feeds into the dynamics of niche contraction and expansion. 

Anolis lemurinus

Anolis allisoni

Island habitat

Mainland habitat