Sexual selection in Hetaerina titia males: a possible key species to understand the evolution of pigmentation in calopterygid damselflies (Odonata: Zygoptera)

Hetaerina titia males bear wing pigmentation patterns similar to Hetaerina and Calopteryx (a derived sister genus of Hetaerina) species: black (typical of Calopteryx) and red (typical of Hetaerina). Sexual selection has operated on red (via male-male competition) and black (via male-male competition and female choice) in Hetaerina and Calopteryx, respectively. We investigated sexual behavior and pigmentation in H. titia to understand their evolution in both genera using H. titia as a possible evolutionary transitional stage. Similar to Calopteryx, the black pigmentation correlated with five male quality aspects: defending a territory, survival, immune ability, parasite resistance and fat reserves. We hypothesize that black pigmentation, but not red, may be used to signal energetic condition when males compete for a territory. The red pigmentation, despite indicating male quality in Hetaerina species, did not correlate with quality but showed a positive relation with parasite burden. These results suggest that the red lost its function which was gained by the black pigmentation, possibly via intrasexual competition, in the absence of female choice (as H. titia does not show male pre-copulatory courtship as in Calopteryx, during which females choose males based on black pigmentation). It is unknown why the red pigmentation was retained.