Natural breakage of the very long intromittent organ of the seed bug Lygaeus simulans (Heteroptera: Lygaeidae)

Liam R Dougherty,David M Shuker

doi:10.14411/eje.2015.098

Abstract

The male intromittent organ of the seed bug Lygaeus simulans ends in a long, sclerotized structure which is used to transfer sperm during mating. Observations suggest that this structure becomes brittle and is liable to breakage after being artificially exposed to the air for an extended period of time. In this study we investigate the frequency of intromittent organ breakage in L. simulans. We first examined the intromittent organ of a sample of males that mated once, and found that breakage was rare. We hypothesised that breakages are likely to be more frequent if a male is able to mate multiple times, and so we next paired males with a female for 21 days in order to provide the opportunity for multiple mating. Almost a quarter (22.5%) of these males exhibited signs of genital breakage. The point of breakage varied: for six males only the tip of the structure (around 6% of its length) was missing, whereas for three males over 50% of the structure was missing. However we were unable to locate any fragments of male genitalia in the reproductive tracts of any females that came into contact with these males. This suggests that breakages do not necessarily occur during mating itself, but instead probably occur as the intromittent organ is being retracted into the genital capsule following mating. In this species breakage may not significantly reduce male reproductive fitness as sperm transfer may still be possible.

Highlights

In many insect taxa the male intromittent organ ends in an elongate, sclerotized tube known as a flagellum or processus gonopori
By allowing males to mate many times during their lifetime, we have shown that a significant proportion of L. simulans males may suffer damage to their intromittent genitalia, breakage of the long, fragile processus gonopori
We were unable to find any fragments of male genitalia in the bursa copulatrix or spermathecal duct of females that came into contact with males exhibiting a breakage

Summary

Introduction

In many insect taxa the male intromittent organ ends in an elongate, sclerotized tube known as a flagellum or processus gonopori This trait is seen for example in Coleo ptera (Rodriguez, 1995; Gack & Peschke, 2005; Matsumura & Yoshizawa, 2010), Hemiptera (Deckert, 1990), Dermaptera (Kamimura, 2005; van Lieshout & Elgar, 2011) and Neuroptera (Sziráki, 2002). The sclerotized nature of such structures means that they may be very fragile and susceptible to breakages, either during intromission or during the deployment/ withdrawal process This will be especially important if breakage significantly impairs a male’s insemination ability, either because the intromittent organ is damaged so as to prevent sperm release, or because the length of the organ is reduced so that it is unable to release sperm in the correct place Though breakage typically renders the copulatory organ non-functional, this strategy is likely favoured because males typically encounter few females and so have limited opportunities to mate (Uhl et al, 2010; Kuntner et al, 2015)

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Conclusion