Reproductive life-history strategies in a species-rich assemblage of Amazonian electric fishes

Abstract

The reproductive biology of only a small fraction of Neotropical freshwater fishes has been described, and detailed comparative studies of reproductive life-history variation in the Neotropical ichthyofauna are lacking. Here we describe interspecific variation in reproductive life history for a multi-species assemblage of the electric knifefish genus Brachyhypopomus (Hypopomidae: Gymnotiformes: Ostariophysi) from Amazonian floodplain and terra firme stream systems. During a year-round quantitative sampling program, we collected and measured key life-history traits from 3,410 individuals. Based on oocyte size distributions, and on circannual variation in gonadosomatic indices, hepatosomatic indices, and capture-per-unit-effort abundance of reproductive adults, we concluded that all species exhibit a single protracted annual breeding season during which females spawn fractionally. We found small clusters of post-larval individuals in one floodplain species and one terra firme stream species, but no signs of parental care. From analyses of body size-frequency distributions and otolith growth increments, we concluded that five species in our study area have approximately one-year (annual) semelparous life history with a single reproductive period followed by death, while two species have a two-year iteroparous life history, with breeding in both year-groups. Despite predictions from life-history theory we found no salient correlations between life history strategy (semelparity or iteroparity) and habitat occupancy (floodplain or terra firme stream). In the iteroparous species B. beebei, we documented evidence for reproductive restraint in the first breeding season relative to the second breeding season and argue that this is consistent with age-regulated terminal investment.

Conservation of migratory fishes in the Amazon basin

“…Reproductive and feeding migrations performed seasonally at the adult stage usually occur each year for most species, which potentially spawn many times during their lives. Most migratory species in the Amazon basin are indeed iteroparous, as opposed to the semelparous reproductive strategy that consists of a single reproductive event during the lifetime, as exemplified by Gymnotiformes in the Amazon basin (Waddell et al, 2019) or more classically by some salmon species (Lucas & Baras, 2001). Some evidence, however, suggests that patterns of migration can change with age.…”

Reproductive effort and terminal investment in a multispecies assemblage of Amazon electric fish

“…We included in our analyses only spawning capable (gonad stage 3 and 4) individuals, following a modified version of the Brown‐Peterson et al (2011) maturational staging scheme (Waddell et al, 2019; Waddell & Crampton, 2018). In so doing, we included all reproductive individuals that had begun to breed but excluded fish with spent gonads; these were mostly restricted to resting individuals of the multiseasonal iteroparous species B. beebei (Waddell et al, 2019). For fish with fractional spawning, stage 4 (actively spawning) females are those in the process of releasing a ripe batch of oocytes, which occurs over several days in Brachyhypopomus (Kirschbaum & Schugardt, 2002), while stage 3 (non‐actively spawning) females are those in the period between successive spawning events, or those that are about to spawn for the first time (Nuñez & Duponchelle, 2009).…”

“…Each site was sampled 1-10 times (usually 2-6 times) per month, for 12 months, with a total effort across all six sites of 193 sampling events and 937 h (Waddell et al, 2019). All sampling was conducted at night, from the end of astronomical twilight until as late as 02:00, during the period of peak electric fish activity.…”

Derived loss of signal complexity and plasticity in a genus of weakly electric fish

“…Despite a high species diversity and wide geographical range, species in the genus Brachyhypopomus (Hypopomidae) ( Fig. 1 ) have been relatively well studied in terms of their evolutionary relationships ( Crampton et al, 2016a , 2016b ) and ecology ( Waddell et al, 2019 ). The EODs have been examined in 18 of the 29 Brachyhypopomus species described.…”