Current projects underway in the Calsbeek lab

My lab's exploration of the selective mechanisms that create diversity rests heavily on an experimental base. Together, we are manipulating the agents of selection that act on lizards (e.g., avian predators excluded from the island on the left by the canopy of no-tangle bird netting). The lab also performes hormonal manipulations to understand the costs of reproduction and populations density manipulations to understand density dependent selection.

Our studies of natural selection have recently turned up some bizarre relationships between the genes that control sire body size and many traits of his offspring. In several cases, we have found that offspring traits that are correlated with sire body size (including size, immune function, running performance) are corrleated differently in sons and daughters. On top of that, natural selection favors alternative expression of these traits depending on whether they show up in males or females. An example of this is shown here. Male lizards experience selection consistent with the trade-off they experience between physiological traits like immune function (swelling) and running endurance (stamina). However, females do not experience the same form of selection. The more we study these patterns, the more it would appear that females should be faced with a dilema when choosing mates, because large sires will produce high quality sons but low quality daughters and small sires will produce high quality daughters but low quality sons. Leave it to mother nature, in another strange twist females typically mate with both large and small sires and then sort out their sperm to produce high quality progeny of each sex!

We have also begun studying a polymorphism in female dorsal pattern. We term these females "diamond" (on the left in the picture), "bar" (lower right), or diamond-bar (intermediates; upper right). Though our breeding studies in the laboratory have shown that the polymorphism is highly heritable, and though our field work suggests that the back patterns may be subject to differing selection pressures, we still understand little about the adaptive significance of this polymorphism. The lab is currently looking into how female morphs differ in reproductive costs (Robert Cox's work), and whether the back patterns are associated with differences in behavior and socially mediated forms of selection.