Tests of hypotheses for morphological and genetic divergence in Megaloprepus damselflies across Neotropical forests

Abstract

Differences in sexual signalling may initiate speciation by limiting gene flow among diverging populations. The damselfly Megaloprepus caerulatus exhibits two, visually obvious 'wing types' across its range. Males from one sub-species have sexually dimorphic, white-banded wings whereas males from the other subspecies lack the sex-specific white wing band. Using mitochondrial (cytochrome c subunit I and 16S) and nuclear (H3) markers, and measures of body size, wing ratio and secondary genitalia, we identified distinct genetic and morphological clades from Mexico to Panama; absence of a wing band was ancestral. To determine if relative reflectance properties of male and female wing tips cue sexual and competitor identity, as they do for wing dimorphic males, we noted reactions of males lacking wing bands to conspecifics with manipulated wings. Isolation by distance explained only 18% of the molecular variation among clades. Relative to wing dimorphic demes, wing monomorphic populations showed lower adult density, lower resource defence and fewer male-male interactions, suggesting lower sexual selection on males. However, not all were less sexually dimorphic in body size. Males lacking wing bands reacted to conspecifics with manipulated wings in ways suggesting that signals for potential mates and competitors do not differ across wing types, a conclusion that awaits more data. Wing mono-and dimorphic demes in Megaloprepus occur allopatrically over relatively short distances and may be isolated via secondary genitalia or unknown physiological constraints. ADDITIONAL KEYWORDS: intraspecific competition-isolation by distance-male mate choice-niche conservatism-Odonata-speciation-sexual signalling-wing polymorphism.