Seminal fluid enhances competitiveness of territorial males' sperm in a fish with alternative male reproductive tactics.

The most common adaptation to sperm competition in males is represented by an increase in the sperm number and/or quality released at mating, to raise their probability of egg fertilization. However, rapidly mounting evidence highlights that seminal fluid may directly influence the competitive fertilization success of a male by affecting either own and/or rival sperm performances. In the black goby, Gobius niger, an external fertilizer with guard-sneaker mating tactics and high sperm competition level, sneaker males' ejaculates contain less seminal fluid and more sperm, that are also of better quality, than those of territorial males. However, territorial males, gain a higher paternity success inside natural nests. Here, we ask whether the seminal fluid can contribute to territorial males' reproductive success by enhancing their sperm performances and/or by decreasing those of sneaker males. Using sperm and seminal fluid manipulation and in vitro fertilization tests, we found that own seminal fluid influences the velocity and fertilization ability of sperm only in territorial males, making them as faster as those of sneakers and with similar fertilization rate. Moreover, both sneaker and territorial males' sperm remain unaffected by the seminal fluid of rival males. Thus, black goby males respond to the different level of sperm competition faced by differently allocating in sperm and non-sperm components of the ejaculate, with sneakers primarily investing in sperm of intrinsic high quality and territorial males relying on the effect of seminal fluid to increase the lower intrinsic quality of their sperm

The influence of mating system on seminal vesicle variability among gobies (Teleostei, Gobiidae)

A variety of sexual selection mechanisms have been implicated to drive the variability of the male reproductive tract in internal fertilizers, while studies on external fertilizers have been largely limited to exploring the influence of sperm competition on testis size and sperm number. Males in the Gobiidae, a speciose teleost family of demersal spawners with external fertilization, are known to be characterized by accessory structures to the sperm duct called seminal vesicles. These seminal vesicles secrete a mucus-enriched seminal fluid. Seminal vesicle size and function have been demonstrated to be influenced by sperm competition at the intraspecific level. With the aim to test the factors influencing the development of these male organs at the interspecific level, an independent contrast analysis was performed on 12 species, differing in mating system type, sperm competition risk, and duration of egg deposition. The type of mating system appears to be the main factor significantly affecting development of seminal vesicles, with males of monogamous species completely lacking or having extremely reduced organs. Riassunto Nelle specie a fecondazione interna e stato ampiamente dimostrato il ruolo di diversi meccanismi di selezione sessuale nel modellare l'estrema variabilita delle strutture genitali maschili. Nelle specie a fecondazione esterna le informazioni sono, invece, limitate principalmente all'influenza della competizione spermatica sulle dimensioni dei testicoli e sul numero di spermi. Nei Gobiidae, famiglia di pesci teleostei caratterizzata da un elevato numero di specie e dalla produzione di uova demerse, i maschi presentano strutture accessorie allo spermidotto, chiamate vescicole seminali, che secernono un liquido seminale particolarmente ricco di mucine. A livello intraspecifico e stato dimostrato come le dimensioni e la funzione delle vescicole seminali sia influenzata dalla competizione spermatica. Con lo scopo di studiare quali fattori a livello interspecifico influenzino lo sviluppo di questi organi, e stata applicata l'analisi comparativa dei contrasti indipendenti a 12 specie di gobidi che differiscono nel sistema riproduttivo, nel livello di competizione spermatica e nella durata della deposizione. L'unico fattore che influenza significativamente lo sviluppo delle vescicole seminali e risultato essere il sistema riproduttivo, infatti nelle specie monogame i maschi non hanno, o hanno estremamente ridotte, vescicole seminali

Females' sampling strategy to comparatively evaluate prospective mates in the peacock blenny Salaria pavo

Emerging evidence suggests the occurrence of comparative decision-making processes in mate choice, questioning the traditional idea of female choice based on rules of absolute preference. In such a scenario, females are expected to use a typical best-of-n sampling strategy, being able to recall previous sampled males based on memory of their quality and location. Accordingly, the quality of preferred mate is expected to be unrelated to both the number and the sequence of female visits. We found support for these predictions in the peacock blenny, Salaria pavo, a fish where females have the opportunity to evaluate the attractiveness of many males in a short time period and in a restricted spatial range. Indeed, even considering the variability in preference among females, most of them returned to previous sampled males for further evaluations; thus, the preferred male did not represent the last one in the sequence of visited males. Moreover, there was no relationship between the attractiveness of the preferred male and the number of further visits assigned to the other males. Our results suggest the occurrence of a best-of-n mate sampling strategy in the peacock blenny

Data from: Tactic-specific differences in seminal fluid influence sperm performance

Seminal fluid often makes up a large part of an ejaculate, yet most empirical and theoretical studies on sperm competition have focused on how sperm characteristics (number and quality) affect fertilization success. However, seminal fluid influences own sperm performance and may potentially influence the outcome of sperm competition, by affecting also that of rivals. As a consequence males may be expected to allocate their investment in both sperm and seminal fluid in relation to the potential level of competition. Grass goby (Zosterisessor ophiocephalus) is an external fertilizer with guard-sneaker mating tactics, where sperm competition risk varies according to the tactic adopted. Here, we experimentally manipulated grass goby ejaculates by separately combining sperm and seminal fluid from territorial and sneaker males. While sperm of sneaker and territorial males did not differ in their performance when they interacted with their own seminal fluid only, sperm of sneakers increased their velocity and fertilization rate in presence of territorial males’ seminal fluid. In contrast, sneaker seminal fluid had a detrimental effect on the performance of territorial males' sperm. Sperm velocity was unaffected by the seminal fluid of males employing the same tactic, suggesting that seminal fluid's effect on rival-tactic sperm is not based on a self/non-self recognition mechanism. Our findings show that cross interactions of sperm and seminal fluid may influence the fertilization success of competing ejaculates with males investing in both sperm and seminal fluid in response to sperm competition risk

Individual adjustment of sperm expenditure accords with sperm competition theory

Sperm competition theory predicts that males should strategically allocate their sperm reserves according to the level of sperm competition, defined as the probability that the sperm of two males compete for fertilizing a given set of ova. Substantial evidence from numerous animal taxa suggests that, at the individual level, sperm expenditure increases when the risk of sperm competition is greater. In contrast, according to the “intensity model” of sperm competition [Parker, G. A., Ball, M. A., Stockley, P. & Gage, M. J. G. (1996) Proc. R. Soc. London Ser. B 263, 1291–1297], when more than two ejaculates compete during a given mating event, sperm expenditure should decrease as the number of competing males increases. Empirical evidence supporting this prediction, however, is still lacking. Here we measured sperm expenditure in two gobiid fishes, the grass (Zosterisessor ophiocephalus) and black goby (Gobius niger), in which up to six sneakers can congregate around the nest of territorial males and release their sperm when females spawn. We show that, in accordance with theory, sneaker males of both species release fewer sperm as the number of competitors increases

Ejaculate traits in relation to male body size in the eastern mosquitofish Gambusia holbrooki

In the present study, the correlation between sperm number, sperm quality (speed, viability, longevity and length), sperm bundles quality (size and dissolving rate) and male body size has been tested in the eastern mosquitofish Gambusia holbrooki a poecilid species characterized by coercive mating tactics where males do not possess obvious ornaments, and the body size is the key determinant of pre-copulatory male mating success. The results do not tally with theoretical predictions. Indeed, no correlation between male body size and either sperm or sperm-bundle traits has been found, evidencing the lack of the theoretically expected trade-off between the investment in characters involved in mate acquisition and the investment in ejaculate quality. An explanation for the observed pattern comes from the extremely dynamic mating system of G. holbrooki, characterized by variable size-related male mating success and strong post-copulatory selective pressure, with all males facing a similar high level of sperm competition. In this situation, a higher investment in growth and maintenance at the expense of ejaculate quality is not expected. These results underscore the necessity to comprehend detailed information on species\u2019 reproductive biology and reproductive environment to understand both the evolution of ejaculate characteristics and possible deviations from theoretical predictions

Differential investment in male accessory glands: lessons from a marine fish with alternative reproductive tactics

Male reproductive accessory glands play a number of important roles, including enhancing fertilization success in competitive contexts. Theory predicts that males experiencing greater sperm competition risk (i.e. those adopting the opportunistic tactic) should invest more in accessory glands and ejaculate. However, empirical data show the opposite pattern; males experiencing lower sperm competition risk (i.e. those adopting the conventional guarder tactic) invest more in accessory glands. This pattern has possibly emerged because these organs also function to optimize sperm economy and sometimes also play a role in parental care, which provides more benefits to guarder males. To tease apart these contrasting patterns, we examined tactic-specific investment in and histology of accessory glands, as well as the effect of their fluids on sperm performance in guarder males, using the plainfin midshipman fish (Porichthys notatus). We found that midshipman accessory glands consist of two distinct structures: nodes and lobules, differing in organization and secretory characteristics both between structures and male types. Like other fishes with alternative reproductive tactics, guarder males invested more in accessory glands and in lobules specifically compared to opportunistic sneaker males. Fluids from both lobule and nodes increased sperm velocity in guarder males. Moreover, guarder males increased their investment in accessory glands across the breeding season. Our results suggest that accessory glands may have multiple functions and may even play a role in parental care and olfactory signalling. Our study emphasizes the diversity in form and function of accessory glands and highlights the importance of these organs in reproduction

JEB data file G. niger.xlsx

Datasheet1. Sperm velocity (VCL) of sneaker and territorial black goby males in different activating solutions (no seminal fluid, own seminal fluid, the seminal fluid of the opposite tactic)<div>Datasheet2. <i>in vitro</i> fertilization success of sneaker and territorial ejaculates <br><br></div