Alternative reproductive tactics and inverse size-assortment in a high-density fish spawning aggregation

Rucha Karkarey,Amod Zambre,Rohan Arthur,Kavita Isvaran

doi:10.1186/s12898-017-0120-5

Abstract

BackgroundAt high densities, terrestrial and marine species often employ alternate reproductive tactics (ARTs) to maximize reproductive benefits. We describe ARTs in a high-density and unfished spawning aggregation of the squaretail grouper (Plectropomus areolatus) in Lakshadweep, India.ResultsAs previously reported for this species, territorial males engage in pair-courtship, which is associated with a pair-spawning tactic. Here, we document a previously unreported school-courtship tactic; where territorial males court multiple females in mid-water schools, which appears to culminate in a unique ‘school-spawning’ tactic. Courtship tactics were conditional on body size, local mate density and habitat, likely associated with changing trade-offs between potential mating opportunities and intra-sexual competition. Counter-intuitively, the aggregation showed a habitat-specific inverse size-assortment: large males courted small females on the reef slope while small males courted equal-sized or larger females on the shelf. These patterns remained stable across two years of observation at high, unfished densities.ConclusionsThese unique density-dependent behaviours may disappear from this aggregation as overall densities decline due to increasing commercial fishing pressure, with potentially large consequences for demographics and fitness.

Highlights

At high densities, terrestrial and marine species often employ alternate reproductive tactics (ARTs) to maximize reproductive benefits
We report unique courtship behaviours in an unfished, high-density spawning aggregation of squaretail groupers (Plectropomus areolatus) that are potentially associated with alternative reproductive tactics (ARTs)
Aggregating males are typically known to court females in small territories, which is often associated with a pair-spawning tactic

Summary

Introduction

Terrestrial and marine species often employ alternate reproductive tactics (ARTs) to maximize reproductive benefits. Karkarey et al BMC Ecol (2017) 17:10 mates, most others will have little success [3] This skew in reproductive success often selects for multiple male and female phenotypes or alternative ways of acquiring reproductive benefits, commonly known as alternative reproductive tactics (ARTs, [4]). High-density conditions could result in significant density-dependent effects such as space limitation and the inability of competitors to fight off multiple intruders [1]. This may lead to a breakdown in mate monopoly [5], lowering the reproductive skew in a population and suppressing the expression of ARTs [6]. The overall population density can impact the strength of sexual selection on male and female traits through its effects on intra-sexual competition [17,18,19,20]

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