The evolutionary history and genetics of morphological traits are the focal research for evolutionary development biology. However, many morphological traits evolve with the change of their related behavioral or physiological traits. The lack of functional aspects of morphological traits makes our understanding on trait evolution incomplete. In my thesis research, I try to bring the evolution of morphological traits and their functional roles together.
In Oriental Drosophila melanogaster species group, male-specific pigmentation on apical wings (wing spots) occurs simultaneously with frontal wing display during courtship (Fig. 1). The role of wing spot was examined in female choice test by removing wing spot physically. It turns out that lack of melanin in apical wing costs males spending longer time to achieve mating in D. biarmipes and D. elegans. Like courtship behavior, this male-specific pigmentation is maintained by sexual selection. The coordination of wing spots and frontal wing display may serve a visual stimulus during courtship.
Fig 1. The materials for my research. A. Phylogeny of Oriental D. melanogaster species group (after Kopp and True, 2002; Prud’homme et al. 2006). In wing display column, + means males display both wings in front of females; – means no frontal wing display; ? means uninvestigated. B. The wing display in D. elegans TP. C. Female (left) and male (right) of D. elegans HK. D. Female (left) and male (right) of D. gunungcola.
Depending on species, male courtship in Drosophila may consist with different types of stimuli, such as auditory, visual, chemical, and mechanical. By conducting the survey on auditory components in studied species group, I found that sound waves produced by male wings during courtship are not coupled with wing spots or frontal wing display. D. biarmipes males produce four types of sound waves during course of courtship. In contrast, males of another wing-spotted species, D. elegans, mute during their courtship. Different stimuli offered by males during courtship evolve independently to each other. The co-occurrence of wing spots and frontal wing display in phylogenetic history represents the functional linkage of these two traits in evolution.
The genetic architecture of trait divergence may reveal partially the history of trait evolution and functional linkage. I use backcross males of D. elegans and D. gunungcola (Fig. 1) to study the genetics responsible for wing spots and courtship evolution. In backcross males from these two species, the wing spot size and courtship are continuously distributed and significantly correlated. The genetic analysis suggests that X chromosome predominantly affect both traits (Fig.2). In order to investigate the genomic region responsible for wing spots and courtship behavior, I am carrying out QTL mapping by using molecular markers.
Fig. 2. The genetic analysis of wing spot size and courtship score in D. elegans backcross males. A is wing spot size, B is courtship score. y and Moe are on X chromosome. White bars are hemizygous or homozygous for elegans alleles. Gray bars are heterozygous for elegans and gunungcola alleles. For t-test on one marker, *** P<0.001, *P<0.05. For ANOVA test, aaa P<0.001, a P<0.05.
