Biogeographic and Genetic Approaches to the Natural History of the Bioluminescent Jamaican Click Beetle, Pyrophorus plagiophthalamus (Coleoptera: Elateridae)

Bioluminescent color in the Jamaican click beetle, Pyrophorus plagiophthalamus, is an ideal system for studies moving from gene to landscape to gain a holistic understanding of the molecular, ecological, and historical basis for adaptation. Previous studies have established the genetics of bioluminescent color variation in this beetle species to the level of the nucleotide base pair in the target gene luciferase. Three different luciferase color alleles affecting ventral light organ color (yellow-green (vYG), yellow (vYE), and orange (vOR)) were found segregating in P. plagiophthalamus populations. These alleles differ from each other in a number of replacement mutations (14 total), the majority of which (11) have a measurable effect on color. Phylogenetic analysis revealed a long-term adaptive trend on Jamaica towards longer wavelength bioluminescence, culminating in the most recently derived vOR allele.

In the first part of this thesis, a study is conducted to isolate and characterize 10 polymorphic microsatellite loci for the Jamaican click beetle. A survey of 36 individuals from three populations in Jamaica showed that the 10 microsatellite loci were highly variable, segregating for 3 to 17 alleles per locus. Observed heterozygosity ranged from 0.250 to 0.917, and mean heterozygosity from 0.601-0.747. Most loci were in Hardy-Weinberg equilibrium, although an excess of homozygotes was observed in four tests (out of twenty), suggesting the possibility of null alleles. Significant linkage disequilibrium was observed between only one pair of microsatellites. These newly developed markers will be useful in understanding the population structure of click beetles on Jamaica and in identifying possible selective factors responsible for bioluminescent color variation. In the second part of the thesis, a study is conducted investigating the historical and geographic context of adaptive color evolution by testing a vicariance model for the origins of ventral organ light color variation in P. plagiophthalamus: that the vOR allele arose and differentiated in an isolated deme on the east side of Jamaica before spreading westward. Comparisons of ventral color phenotypes, luciferase coding and intron sequences, mtDNA, and microsatellite data provided evidence for past population subdivision on Jamaica and ongoing gene flow, as has been found for other island endemics. However, the pattern of differentiation supported the allopatric divergence of vYG and vYE alleles. The vOR gene appears to have arisen relatively recently from a vYE precursor and postdates the period of major biogeographic isolation dating ~1.75MYA. The implications of the study are discussed for discerning ecological causation in the adaptive sequence from nucleotide to landscape to population change for bioluminescent color. The results present a foundation for further ecological studies testing the causal basis for bioluminescent color variation on Jamaica for this colorful model system of natural selection in action.