Mating and ejaculate allocation pattern in the kelp crab Taliepus dentatus (Decapoda: Epialtidae)

Katrin Pretterebner,Jorge López,Javiera Sanhueza,Luis Miguel Pardo

doi:10.1590/2358-2936e2021012

Abstract

Ejaculate allocation patterns vary widely among species and often depend on characteristics of the individual. However, it is poorly known whether ejaculate allocation patterns change in response to distinct ontogenetic stages (i.e., adolescent vs. adult). The present study aims to describe the mating process and test variations in ejaculate allocation in response to the ontogenetic stage of the Chilean kelp crab Taliepus dentatus (H. Milne Edwards, 1834). Mating consists of the following sequence: (1) pre-copulatory guarding (i.e., male grasping female and/or caging female between legs), (2) copulation in sternum-to-sternum position, and (3) post-copulatory guarding (i.e., male grasping female or carrying her around by the chelae). The mating behavior and ejaculate allocation pattern differed between the two contrasting male ontogenetic stages. Adolescent males generally delivered less ejaculate in repeated short copulations and adult males transferred more ejaculate in a single extended copulation. Ejaculate allocation in adolescents was dependent on female size, but not so in adults. Variation in the ejaculate allocation pattern may be common in species with contrasting male ontogenetic stages, where less competitive males (i.e., adolescents) economize their limited seminal reserves. Conversely, adults which have a greater capacity to produce seminal material (fluids + spermatozoa) may invest greater quantities of seminal material.

Highlights

Ejaculate allocation strategies and prudent ejaculate expenditure aim to maximize the reproductive output and are present in males of many taxa of terrestrial insects, birds, and fishes (Wedell et al, 2002) as a response to energetically costly production of seminal materials, especially seminal f luids (Dewsbury, 1982)
This study aims to describe the mating process in T. dentatus and understand the influence of the individual ontogenetic stage on the quantity of seminal material transferred from the male to the female during copulation
The vasosomatic index (VSI) represents the capacity of males to transfer seminal material with respect to their size (Sainte-Marie, 2007; Pardo et al, 2015) and fluctuation of the VSI can be interpreted as the condition of males during the reproductive cycle, indicating periods of mating and seminal reserve recovery (Pardo et al, 2019)

Summary

Introduction

Ejaculate allocation strategies and prudent ejaculate expenditure aim to maximize the reproductive output and are present in males of many taxa of terrestrial insects, birds, and fishes (Wedell et al, 2002) as a response to energetically costly production of seminal materials, especially seminal f luids (Dewsbury, 1982). Ejaculate allocation refers to the ability of males to adjust the amount of ejaculate transferred to females. The pattern of allocation of spermatozoa varies widely among species and depends on characteristics of the individual as well as the socio-sexual context. Males may modify the amount of spermatozoa delivered to females in response to the socio-sexual context, notably by adjusting ejaculate size to match the risk of sperm competition (Wedell et al, 2002). In spider crabs (Majoidea) in particular, male ejaculate allocation patterns have been poorly studied, except for Chionoecetes opilio 1788) (Sainte-Marie and Lovrich, 1994; Rondeau and Sainte-Marie, 2001; Sainte-Marie et al, 2002)

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