Ejaculate Allocation and Sperm Characteristics Differ among Alternative Male Types in a Species of Fish with Cooperation and Competition among Unrelated Males

Abstract

Sexual selection arising from sperm competition has driven the evolution of immense variation in ejaculate allocation and sperm characteristics not only among species, but also among males within a species. One question that has received little attention is how cooperation among males affects these patterns. Here we ask how male alternative reproductive types differ in testes size, ejaculate production, and sperm morphology in the ocellated wrasse, a marine fish in which unrelated males cooperate and compete during reproduction. Nesting males build nests, court females and provide care. Sneaker males only “sneak” spawn, while satellite males sneak, but also help by chasing away sneakers. We found that satellite males have larger absolute testes than either sneakers or nesting males, despite their cooperative role. Nesting males invested relatively less in testes than either sneakers or satellites. Though sneakers produced smaller ejaculates than either satellite or nesting males, we found no difference among male types in either sperm cell concentration or sperm number, implying sneakers may produce less seminal fluid. Sperm tail length did not differ significantly among male types, but sneaker sperm cells had significantly larger heads than either satellite or nesting male sperm, consistent with past research showing sneakers produce slower sperm. Our results highlight that social interactions among males can influence sperm and ejaculate production.

Sperm competition experiments reveal low prezygotic postmating isolation between parasitic and nonparasitic lamprey ecotypes

“…Alternatively, there might be a trade‐off between sperm concentration and sperm quality, as L. planeri males may strongly invest in sperm numbers at the cost of a lower sperm quality (Snook, 2005 ). A trade‐off may also occur between sperm velocity and sperm morphology as observed in ocellated wrasses where sneaker males have sperm cells with larger heads than satellite or nesting males and their sperm are also slower (Alonzo et al, 2021 ).…”

“…Sperm longevity could influence fertilization success notably when gamete release by males and females is not synchronous (Staponkus & Kesminas, 2014 ). In addition, the morphology of sperm could also be compared between L. fluviatilis and L. planeri as it might influence sperm velocity and siring success (Alonzo et al, 2021 ).…”

Molecular, behavioural and morphological comparisons of sperm adaptations in a fish with alternative reproductive tactics

“…In other fish species, differences in sperm shape can be found between male morphs. For example, in the ocellated wrasse ( Symphodus ocellatus ), sneaker males had larger sperm heads, compared with nesting males and satellite males, while tail length did not differ between the three types of males (Alonzo et al, 2021 ).…”

Evolutionary trade-offs between testes size and parenting in Neotropical glassfrogs

“…Studies on the role of paternal care in the evolution of testes size have reported contrasting results; that is, negative covariation in some taxa (e.g. birds [ 20 ], mammals [ 21 ] or fish [ 42 ]), a positive correlation in others (e.g. cuckoos [ 43 ]) or no association (e.g.…”