Use of noninvasive 'bug-eggs' to enable comparative inferences on genetic mating system with and without parental information: A study in a cattle egret colony.

Carolina Isabel Miño,Talita Alvarenga Valdes,Elaine Dantas De Souza,Vera Lúcia Cortiço Corrêa Rodrigues,Sílvia Nassif Del Lama,Emmanuel Moralez-Silva,Lorenzo Zane

doi:10.1371/journal.pone.0183153

Abstract

Colonial waterbirds such as herons, egrets and spoonbills exhibit ecological characteristics that could have promoted the evolution of conspecific brood parasitism and extra-pair copulation. However, an adequate characterization of the genetic mating systems of this avian group has been hindered by the lack of samples of elusive candidate parents which precluded conducting conventional parentage allocation tests. Here, we investigate the genetic mating system of the invasive cattle egret using hematophagous insects contained in fake eggs to collect blood from incubating adults in a wild breeding colony. We tested a protocol with a previously unused Neotropical Triatominae, Panstrongylus megistus, obtained blood samples from males and females in 31 nests built on trees, drew blood from 89 nestlings at those nests, and genotyped all samples at 14 microsatellite loci, including six new species-specific loci. We comparatively addressed the performance of parentage allocation versus kinship classification of nestlings to infer the genetic mating system of cattle egrets. In line with previous behavioral observations, we found evidence in support of a non-monogamous genetic mating system, including extra-pair paternity (EPP) and conspecific brood parasitism (CBP). Parentage allocation tests detected a higher percentage of nests with alternative reproductive tactics (EPP: 61.7%; CBP: 64.5%) than the kinship classification method (EPP: 50.0%; CBP: 43.3%). Overall, these results indicate that rates of alternative reproductive tactics inferred in the absence of parental genetic information could be underestimated and should be interpreted with caution. This study highlights the importance of incorporating samples from candidate parents to adequately determine the genetic mating system of a species. We expand knowledge on the reproductive tactics of colonial waterbirds, contributing novel data on the genetic mating system of the cattle egret, valuable for the design of management strategies for this invasive bird.

Highlights

Mating systems, i.e., the way in which females and males organize during breeding seasons, are dynamic and can be remarkably variable among species and populations, as well as within populations [1]
The results revealed that both analytical approaches generally agreed in evidencing alternative reproductive tactics, but the rates of inferred alternative behaviors varied depending on the method used (Table 2, Fig 2)
This study presents the first application of the ‘bug-egg’ method to inspect the genetic mating system of a colonial tree-nesting bird

Summary

Introduction

I.e., the way in which females and males organize during breeding seasons, are dynamic and can be remarkably variable among species and populations, as well as within populations [1]. The adequate characterization of the actual mating system of a species requires that genetic studies are carried out as a complement to field observations on social reproductive behavior. The genetic mating system of a species is usually inferred by conducting conventional DNA-based parentage allocation tests, based on the comparison of the genotypes of attending adults and those of the progeny [5]. Such methods have revealed that alternative reproductive strategies, such as extra-pair copulations (EPC) and conspecific brood parasitism (CBP)–when a female lays eggs in the nests of another female–are fairly common in passerines and non-passerines [2,6,7]

Objectives

Methods

Results

Discussion

Conclusion