Birth date predicts alternative life‐history pathways in a fish with sequential reproductive tactics

Abstract

Summary In species with plastic expression of alternative reproductive tactics (ARTs), individuals of the same sex, usually males, can adopt different reproductive tactics depending on factors such as body size. The ‘birth date hypothesis’ proposes that condition‐dependent expression of ARTs may ultimately depend on birth date, because individuals born at different times of the year may achieve different sizes and express different reproductive tactics accordingly. However, this has rarely been tested. Here, we tested this hypothesis in a fish with ARTs, the peacock blenny (Salaria pavo). A long‐term (6 years) mark–recapture study demonstrated that ARTs in the peacock blenny were sequential and that males may follow at least two alternative life‐history pathways: a nest‐holder pathway, in which males express the nest‐holder tactic from their first breeding season onwards, and a parasitic pathway, where males reproduce on their first breeding season as sneaker males and subsequently as nest‐holders. We have found evidence of a birth date effect on the expression of ARTs in the peacock blenny. Males following the nest‐holder pathway are born earlier and are larger at the first breeding season than males following the parasitic pathway, but they have similar growth curves. The mechanisms underlying a birth date effect are far from clear and might be diverse. We have not found support for a mechanism of body size threshold triggering sexual maturation and subsequent ARTs. A mechanism of tactic determination that is strictly based on timing of first maturation is also unlikely. A proxy of lifetime reproductive success shows crossing (body size associated) fitness curves for the two main life‐history pathways.

Evidence for ontogenetically and morphologically distinct alternative reproductive tactics in the invasive Round Goby Neogobius melanostomus

“…We, however, only found a small proportion of intermediates (9%). Fagundes et al [46] also found a small proportion of intermediates or transient individuals (7%) in Peacock Blenny, Salaria pavo . In this long-term mark-recapture study, it was found that intermediates express a sneaker tactic and switch to the nest-holder or parental tactic within their first breeding season [46].…”

“…Fagundes et al [46] also found a small proportion of intermediates or transient individuals (7%) in Peacock Blenny, Salaria pavo . In this long-term mark-recapture study, it was found that intermediates express a sneaker tactic and switch to the nest-holder or parental tactic within their first breeding season [46]. While we cannot tell when tactics are fixed, because we did not follow fish for any length of time, our data do suggest that tactics in the Round Goby are fixed before the breeding season.…”

“…parentals) and were larger at the start of their first breeding season, as compared to males born later in the season [46]. This ‘birthdate effect’ is proposed in species where reproductive success is related to body size and where alternative reproductive tactics are dependent on environmental and/or physical conditions [11].…”

“…Individuals born in the same year at different periods will thus have a different body size at the start of their first breeding season [11]. When born early in the season, individuals can become parental males at the start of their breeding season [46], or they can start by adopting a sneaking tactic [47,48]. In salmonids it was found that individuals that grow quicker and mature at an earlier age adopt a sneaking tactic (“jacks”) [48].…”

Maternal basking regime has complex implications for birthdate and offspring phenotype in a nocturnally foraging, viviparous gecko

“…Examples exist across varied taxa and parity modes, including an association of early birthdate with adoption of an alternative reproductive tactic in male fish (Fagundes et al, 2015), with greater survival and larger mass at first summer's end in penguin chicks (Stier et al, 2014), and with greater survival (at high population density) in squirrels (Williams et al, 2014). In principle, effects on offspring from time of birth may arise from: (1) seasonal variation in the quality of the environment into which offspring are born; (2) variation in the quality of offspring themselves, arising from prenatal developmental effects; and (3) in those species that provide it, variation in parental care during the postnatal period (Wapstra et al, 2010;Stier et al, 2014).…”