The evolution of copulation frequency and the mechanisms of reproduction in male Anolis lizards

Abstract

The evolution of many morphological structures is associated with the behavioral context of their use, particularly for structures involved in copulation. Yet, few studies have considered evolutionary relationships among the integrated suite of structures associated with male reproduction. In this study, we examined nine species of lizards in the genus Anolis to determine whether larger copulatory morphologies and higher potential for copulatory muscle performance evolved in association with higher copulation rates. In 10–12 adult males of each species, we measured the size of the hemipenes and related muscles, the seminiferous tubules in the testes, and the renal sex segments in the kidneys, and we assessed the fiber type composition of the muscles associated with copulation. In a series of phylogenetically-informed analyses, we used field behavioral data to determine whether observed rates of copulation were associated with these morphologies.We found that species with larger hemipenes had larger fibers in the RPM (the retractor penis magnus, a muscle that controls hemipenis movement), and that the evolution of larger hemipenes and RPM fibers is associated with the evolution of higher rates of copulatory behavior. However, the sizes of the seminiferous tubules and renal sex segments, and the muscle fiber composition of the RPM, were not associated with copulation rates. Further, body size was not associated with the size of any of the reproductive structures investigated. The results of this study suggest that peripheral morphologies involved in the transfer of ejaculate may be more evolutionarily labile than internal structures involved in ejaculate production.

Genital morphology associated with mating strategy in the polymorphic lizard, Uta stansburiana

“…Therefore, it is possible that the apical horn could provide a fitness advantage for usurper morphs, or may be tied to other behavioral differences across morphs, such as copulation duration. Larger hemipenes have been correlated with more frequent copulation rates in Anolis lizards (Johnson et al ) and longer and more complex longer hemipenes are associated with greater copulation duration in gartersnakes (King et al ). Morph‐specific mating behavior could drive differences in relative hemipenis length and ornamentation.…”

Use it and bruise it: copulation rates are associated with muscle inflammation across anole lizard species

“…To determine the natural copulation rates of a group of 22 anole species (Table 1), we conducted focal observations during the summer breeding seasons of 2004–2015 (Johnson et al, 2014). For these 22 species, we conducted ~ 11:00 h of observation on 1200 lizards, observing a median of 37 males per species (range: 7–113) for a median of 41 h per species (range: 8.2–123.3 h).…”

“…Copulation occurs when a male mounts a female, orients his pelvis to align with hers, and everts a hemipenis into her cloacal vent (Crews, 1978; Shine et al, 2000). Yet even among closely related species, there is substantial variation in the frequency of copulation (Johnson et al, 2014) and in the size of the hemipenes (Dowling & Savage, 1960; Arnold, 1986). Thus, squamates offer a group across which a pair of muscles contracts in a single behavioral context, but their frequency of use and the contractile force required (i.e.…”

Does male gonopodial morphology affect male-female mating positioning in the livebearing fish Xenophallus umbratilis?

“…How copulation occurs in sexually reproducing organisms has garnered much attention, and this process is well documented in mammals [1][2][3], birds [4][5][6], reptiles [7][8][9], and some insects [10,11]. Copulation is not common in fishes, though internal fertilization is known to occur in sharks and rays [12], phallostethids [13], and goodeids [14], but is most often studied in the livebearing poeciliid fishes [15].…”