Size not such a big thing for seed bugs

March 03, 2016

By the looks of it, size should be a big thing when it comes to seed bugs mating, but it only matters when more than one mating partner is around to choose from. That is what researchers Liam Dougherty and David Shuker of the University of St Andrews in Scotland found when investigating the mating strategies of two closely related black and red coloured seed bugs. The male sexual organs of these insects can be up to two-thirds the length of their bodies. The findings are published in Springer's journal Behavioral Ecology and Sociobiology.

Animal genitalia vary greatly in size and complexity across species, and the reasons why specific sizes or shapes of genitals are preferred can be complex. To this end, Dougherty and Shuker set out to analyse the specifics behind mate selection and fertility success in two seed bug species, Lygaeus equestris and Lygaeus simulans. The males of both species have very long external sexual organs which end in a hollow tube called the processus. At around 7 millimetres long, the processus is used to ejaculate sperm into a female and can stretch to two-thirds the length of a male's body. Why the processus has evolved to be so long in the first place is still unclear, though the extreme length would suggest that sexual selection has played a role in its evolution.

Two experiments were carried out to assess if males with a longer processus were either more likely to mate with a female, or more likely to fertilise a female's eggs during mating. The social context in which mating takes place was also assessed, to see whether the presence of more than one male or female influenced how important processus length is for males both before and during mating.

Dougherty and Shuker found that processus length did have an influence on a male's chances of mating in one of the species (L. equestris), but only in certain contexts. Processus length was most important when a rival male was present during a mating trial. This finding has relevance, because it suggests that in the wild the strength of selection on processus length will depend on the number of males competing to mate with each female.

The length of the processus is also important during mating for both species. This is because males commonly fail to fertilise any of a female's eggs during mating. In fact, the authors show that males with a medium-length processus are the most likely to successfully fertilise a female. Therefore in both species bigger isn't necessarily better when it comes to genital length.

"The length of the penis in two species of seed bug is subject to complex patterns of selection, varying depending on the social context and whether selection is measured before or after mating," said Dougherty in summarising the findings.

"Our results highlight the fact that genitalia may be subject to both direct and indirect selection at different stages of mating, and that to fully understand the evolution of such traits we should combine estimates of selection arising from these multiple episodes," elaborated Shuker.
-end-
Reference: Dougherty, L.R. & Shuker, D.M. (2016). Variation in pre- and post-copulatory sexual selection on male genital size in two species of lygaeid bug, Behavioral Ecology and Sociobiology
DOI 10.1007/s00265-016-2082-6

Springer

Related Species Articles from Brightsurf:

A new species of spider
During a research stay in the highlands of Colombia conducted as part of her doctorate, Charlotte Hopfe, PhD student at the University of Bayreuth, has discovered and zoologically described a new species of spider.

Two new species of parasite discovered in crabs -- discovery will help prevent infection of other marine species
Two new species of parasite, previously unknown to science, have been discovered in crabs in Swansea Bay, Wales, during a study on disease in the Celtic and Irish Seas.

Marine species are outpacing terrestrial species in the race against global warming
Global warming is causing species to search for more temperate environments in which to migrate to, but it is marine species -- according to the latest results of a Franco-American study mainly involving scientists from the CNRS, Ifremer, the Université Toulouse III-Paul Sabatier and the University of Picardy Jules Verne -- that are leading the way by moving up to six times faster towards the poles than their terrestrial congeners.

Directed species loss from species-rich forests strongly decreases productivity
At high species richness, directed loss, but not random loss, of tree species strongly decreases forest productivity.

What is an endangered species?
What makes for an endangered species classification isn't always obvious.

One species, many origins
In a paper published in Nature Ecology and Evolution, a group of researchers argue that our evolutionary past must be understood as the outcome of dynamic changes in connectivity, or gene flow, between early humans scattered across Africa.

Species on the move
A total of 55 animal species in the UK have been displaced from their natural ranges or enabled to arrive for the first time on UK shores because of climate change over the last 10 years (2008-2018) -- as revealed in a new study published today by scientists at international conservation charity ZSL (Zoological Society of London).

Chasing species' 'intactness'
In an effort to better protect the world's last ecologically intact ecosystems, researchers developed a new metric called 'The Last of the Wild in Each Ecoregion' (LWE), which aimed to quantify the most intact parts of each ecoregion.

How do species adapt to their surroundings?
Several fish species can change sex as needed. Other species adapt to their surroundings by living long lives -- or by living shorter lives and having lots of offspring.

Five new frog species from Madagascar
Scientists at Ludwig-Maximilians-Universitaet in Munich and the Bavarian State Collection of Zoology have named five new species of frogs found across the island of Madagascar.

Read More: Species News and Species Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.