Date: July 16 2014
Source: Behavioral Ecology and Sociobiology
Charles Darwin proposed that sexual selection through mate
choice is a huge factor driving evolutionary change. As a result, females have
since been identified as the choosier sex, as they select mates on
ornamentation. Over the past decade, however, scientists have gathered evidence
refuting this position. Male mate choice has been documented in species of
birds, fish, lizards, insects, and mammals. Although male mate choice is being
recognized, there are still doubts that it can select for female ornamentation,
as costly displays would be in competition with egg production. Female
ornamentation has developed when the benefits outweighed this cost – such as in
gift-giving species, where the males provide females with a gift during mating
that can be helpful for their survival.
Cabbage
butterfly males donate a protein-rich spermatophore that makes up 10% of their
body weight. This is a substantial reproductive investment, but it is likely to
result in high reward, as it significantly increases female reproductive
output. Wing coloration of the cabbage butterfly depends on the deposition of
nitrogen-rich pigments called Pteridines; they depend on larval acquisition of
nitrogen and are therefore considered costly. The involvement of Pteridine in
wing coloration has been shown to provide males with mating advantage, but
until this study was conducted the adaptive importance of Pteridine in female
wings had not been considered.
A July 2014
study tested whether pteridine-based wing coloration in females is subject to
sexual selection via male mate choice. Previous studies showed that male
cabbage butterflies respond to visual stimuli on the females’ ventral
hindwings. The researchers used reflectance spectrometry in order to assess
wing coloration on a two millimeter diameter spot on the ventral left hindwings
of female cabbage butterflies. They then assigned virgin female cabbage
butterflies into two groups – pteradine-extracted and control. For the
butterflies in the pteradine-extracted group, the researchers used NaOH to
remove the pteradine pigment from the two millimeter section of wing, not
altering any other morphological characteristics. The control group was then
submerged in isopropanol in order to control for any handling effects.
The
researchers conducted the trials by presenting each male with one
pteradine-extracted female and one control female. They then recorded the
number of copulation attempts and male mating approaches towards each female.
The researchers found that males were more likely to direct a mating approach
toward a control female, indicating that sexual selection is occurring to
select for female ornamentation in the cabbage butterfly.
Citation: Tigreros,
Natasha, Monica A. Mowery, and Sara M. Lewis. "Male Mate Choice Favors
More Colorful Females in the Gift-giving Cabbage Butterfly." Behavioral
Ecology and Sociobiology (2014): n. pag. Springer. Web. 5 Feb. 2015.
Allie,
ReplyDeleteI think your article takes an interesting spin on sexual selection. There are lots of examples in which females choose males, but I like how your article brings up the fact that there are instances of males choosing females. Also your article briefly mentions that sexual selection has a price, which is the main focus of my article on male guppies.
Hey Allie,
ReplyDeleteI thought it made sense for males to be given the power to choose their mates in this particular scenario. Usually, most examples involve females choosing male mates based on the attractiveness of the mate. In other words, they sexually select for their partner. They are able to do so as the evolution of their species weighs in large part on the ability of females to reproduce. As they have more to offer, they are in control of choosing a mate. However, in this situation, the males have a more significant contribution to the evolution of their species than the females as they are not only contributing sperm but also a protein that increases the reproductive output, as you mentioned. So, in the end, the main gender in control of sexual selection boils down to what the organisms have to offer. Though usually nothing seems to be able to top the ability to produce offspring, occasionally a superior trait may occur.
Hey Allie,
ReplyDeleteI found this article quite interesting because we are all taught about how females are particular in choosing males in species, but this particular article portrays the perfect example in which this happens with the opposite genders. It is common knowledge that males also are particular in choosing females in particular species, but this article does a good job in showing how female ornaments play a key role rather than examples looked at before with male ornaments. This article proves that sexual selection can play a vital role in mate choice for both genders in species.
Hey Allie,
ReplyDeleteThis article was one of the first I came across that focuses on sexual selection where the male has a say and picks for female ornamentation. I found it especially interesting that the males in this case are willing to give up 10% of their body weight for the continuation of their species. That is a really big investment and this clearly shows how sexual selection is much stronger than natural selection in this case.