Morphological variation and reproductive isolation in the Hetaerina americana species complex

Abstract

Incomplete premating barriers in closely related species may result in reproductive interference. This process has different fitness consequences and can lead to three scenarios: niche segregation, sexual exclusion, or reproductive character displacement. In morphologically cryptic species, isolation barriers can be difficult to recognize. Here, we analyzed the morphological, behavioral, and genetic differences between two sympatric cryptic species of the genus Hetaerina to determine the characters that contribute the most to reproductive isolation and the effect of the high rates of behavior interference between the species. We found complete genetic isolation and significant differences in the morphometry of caudal appendages and wing shape, as well as body size variation between species. In contrast, we did not find clear differences in the coloration of the wing spot and observed high rates of interspecific aggression. Our results suggest that divergence in the shape of the caudal appendages is the principal pre-mating barrier that prevents interspecific mating. Moreover, a scenario of character displacement on body size was found. Nevertheless, size could play an important role in both inter- and intrasexual interactions and, therefore, we cannot differentiate if it has resulted from reproductive or aggressive interference.

Genomic differentiation and niche divergence in the Hetaerina americana (Odonata) cryptic species complex

“…This indicates that gene flow is null among the three taxa even when there is co-occurrence at some localities (e.g., EF, Za, Ve, CC, NR; Figure 1). Furthermore, we found that H. calverti is the most divergent taxon and that, in agreement with previous findings (Vega-Sánchez et al, 2022), it…”

“…This indicates that gene flow is null among the three taxa even when there is co‐occurrence at some localities (e.g., EF, Za, Ve, CC, NR; Figure 1). Furthermore, we found that H. calverti is the most divergent taxon and that, in agreement with previous findings (Vega‐Sánchez et al., 2022), it shows complete genetic isolation from the other two. In contrast, the two groups of H. americana (North and South) showed evidence of a lower degree of divergence; however, the patterns of genetic differentiation allowed us to recognize them as two discrete taxa, except for two populations (EF and SN) that showed some mixed ancestry, which can be associated to incomplete or weaker isolation barriers between these two taxa, as are ecological barriers (Sánchez‐Guillén et al., 2012).…”

“…americana South (Vega-Sánchez et al, 2022). In contrast, the isolation barriers between H. americana North and South seem to be different, since the divergence in the shape of caudal appendages is subtler (Vega-Sánchez et al, 2019).…”

“…Morphological variation in caudal appendages is known to play an important role as a premating mechanical isolation barrier in odonates such as Enallagma , Ischnura and Hetaerina (McPeek et al., 2011; Sánchez‐Guillén et al., 2012). The differentiation in the shape of the male caudal appendages is more conspicuous in H. calverti and it is considered the main morphological character that contributes to reproductive isolation in localities where it is sympatric with H. americana South (Vega‐Sánchez et al., 2022). In contrast, the isolation barriers between H. americana North and South seem to be different, since the divergence in the shape of caudal appendages is subtler (Vega‐Sánchez et al., 2019).…”

“…Additional analyses indicated that H. calverti is reproductively isolated from the other two taxa by mechanical barriers related to the shape of caudal appendages (Vega‐Sánchez et al., 2022). However, morphological variation in these structures is less conspicuous between H. americana North and South, suggesting that the three entities represent different stages of the speciation continuum and that other isolation mechanisms besides mechanical barriers could be present.…”