Characteristics of breeding habitat, genetic mating system, and determinants of male mating success in the sponge-dwelling goby Elacatinus lori

Determining the patterns and causes of variation in reproductive success is key to understanding mating systems and sexual selection, but they are challenging to study in cryptobenthic coral reef fishes. Here, we investigate characteristics of breeding habitat, the genetic mating system, and correlates of male mating success in the neon goby Elacatinus lori. This fish is primarily found living and breeding within the yellow tube sponge Aplysina fistularis in Belize - it has become a focus of marine population ecology research, but knowledge of its behavioral ecology is lacking. First, we show that sponges occupied by breeding males tend to be larger than those occupied by residents. Second, we show that E. lori males exhibit a polygynous mating system: some males breed with multiple females simultaneously and/or sequentially. Third, we show that male size is positively related to multiple metrics of male mating success: number of days paired with females, number of clutches laid, and total reproductive output. Male size, however, explains only a small proportion of the variation in male mating success, suggesting that other aspects of the males' phenotype and ecological context need to be quantified to better explain variation in mating success. More generally, our results suggest that when female movements are restricted, it is necessary to measure habitat characteristics and male traits at smaller spatial scales to gain a deeper understanding of their effects on mating systems and sexual selection. Significance statement Measuring male reproductive success in a wild population is notoriously difficult, particularly in cryptobenthic coral reef fishes. Often, mating success is used as a proxy for reproductive success because it is easier to measure. Variation in mating success is often predicted by characteristics of the individual and its breeding habitat. Here, we simultaneously describe the (i) breeding habitat, (ii) genetic mating system, and (iii) relationship between male traits, habitat characteristics, and mating success in the neon goby Elacatinus lori. By investigating these three elements together, we provide solid foundations for understanding this species' mating system. More generally, we suggest that investigations of variation in mating success may be improved by approaching analyses at smaller, more biologically relevant, spatial scales. Our findings highlight the challenges and opportunities of investigating mating systems of cryptobenthic coral reef fishes in the wild.

Automated summary

Determining patterns and causes of variation in reproductive success is crucial for understanding mating systems and sexual selection. This study focused on the cryptobenthic coral reef fish Elacatinus lori to investigate its breeding habitat characteristics, genetic mating system, and factors influencing male mating success. The results showed a positive relationship between male size and multiple metrics of mating success, but only explained a small proportion of the variation, suggesting the need to quantify other aspects of male phenotype and ecological context. The study emphasizes the importance of measuring habitat characteristics and male traits at smaller spatial scales to gain a deeper understanding of mating systems and sexual selection in species with restricted female movements.