How relatedness between mates influences reproductive success: An experimental analysis of self-fertilization and biparental inbreeding in a marine bryozoan.

Scott C Burgess,Marília Bueno,Lisa Sander

doi:10.1002/ece3.5636

Abstract

Kin associations increase the potential for inbreeding. The potential for inbreeding does not, however, make inbreeding inevitable. Numerous factors influence whether inbreeding preference, avoidance, or tolerance evolves, and, in hermaphrodites where both self‐fertilization and biparental inbreeding are possible, it remains particularly difficult to predict how selection acts on the overall inbreeding strategy, and to distinguish the type of inbreeding when making inferences from genetic markers. Therefore, we undertook an empirical analysis on an understudied type of mating system (spermcast mating in the marine bryozoan, Bugula neritina) that provides numerous opportunities for inbreeding preference, avoidance, and tolerance. We created experimental crosses, containing three generations from two populations to estimate how parental reproductive success varies across parental relatedness, ranging from self, siblings, and nonsiblings from within the same population. We found that the production of viable selfed offspring was extremely rare (only one colony produced three selfed offspring) and biparental inbreeding more common. Paternity analysis using 16 microsatellite markers confirmed outcrossing. The production of juveniles was lower for sib mating compared with nonsib mating. We found little evidence for consistent inbreeding, in terms of nonrandom mating, in adult samples collected from three populations, using multiple population genetic inferences. Our results suggest several testable hypotheses that potentially explain the overall mating and dispersal strategy in this species, including early inbreeding depression, inbreeding avoidance through cryptic mate choice, and differential dispersal distances of sperm and larvae.

Highlights

In many species of plants and animals, organisms settle and breed near kin
More recent analyses on biparental inbreeding have focused on animals with separate sexes to explain inbreeding avoidance, preference, or tolerance
Despite the potential for self‐fertilization in bryozoans, and early studies on bryozoans even suggesting that selfing was widespread and the predominant mode of sexual reproduction, available evidence suggests that outcrossing is common in bryozoans (Hoare & Hughes, 2001; Hunter & Hughes, 1993; Ryland & Bishop, 1993; Silén, 1972; Temkin, 1994; Yund & McCartney, 1994)

Summary

| INTRODUCTION

In many species of plants and animals, organisms settle and breed near kin. Such kin associations increase the potential for inbreed‐ ing (mating with relatives; Wright, 1943). More recent analyses on biparental inbreeding have focused on animals with separate sexes to explain inbreeding avoidance (where mates are less related than expected under random mating), preference (where mates are more related than expected under random mat‐ ing), or tolerance (where inbreeding occurs to the degree expected from random mating; Duthie & Reid, 2016; Szulkin et al, 2013). The capacity to avoid or prefer inbreeding will de‐ pend on the ability of individuals to discriminate among relatives and unrelated conspecifics, which will depend on the degree and range of relatedness between potential mates, the genetic basis of any self‐ incompatibility mechanism, and the structural characteristics of the mating system that determine the mode and timing of gamete trans‐ fer (Duthie & Reid, 2016; Eckert, 2011; Jarne & Charlesworth, 1993; Kelly & Willis, 2002; Lloyd & Schoen, 1992). Reproductive success is esti‐ mated by the number of larvae that are released and successfully metamorphose

| METHODS

Findings

| DISCUSSION