It is often the case that sexual dimorphism in animals leaves the males more colourful and with extra appendages that are used to impress females. However this is not the case in socially monogamous birds, such as the Blue-footed Booby, Sula nebouxii.

Both male and female Blue-footed Booby’s both have brightly coloured blue feet used during courtship. The reasons behind the females having ornamental structures like the males have seldom been documented. In this case it is in the interest of both the females and males to have nice blue feet.

A study has found that the bluer and brighter a females feet, the more attractive she is to the males. Through an experiment of temporarily changing females feet to a duller shade of blue, scientists found that they received less intra- and extrapair courtship than the control females. They concluded that the blue colour of the feet is favoured by sexual selection through male preference.

In a similar study, the opposite was tested. Scientists found that the brightness of the males feet colour was related to the overall health of the bird. When deprived of food for 48hrs, the blue colour became duller as an indication of its ill health. This study also found that this had an influence on how much reproductive investment the female put in.  After the first egg was laid, the male responsible was taken and his feet were temporarily modified to appear duller and less attractive. In response females decreased the size of their second egg as their partner appeared to be in ill condition. They concluded that female Blue-footed Booby’s continually evaluate the health of their partners to determine the amount of their reproductive investment.

References

Torres R & Velando A. (2005). Male preference for female foot colour in the socially monogamous blue-footed booby, Sula nebouxii. Animal Behaviour, 69(1), 59-65.

Velando A, Beamonte-Barrientos R & Torres R. (2006). Pigment-based skin colour in the blue-footed booby: an honest signal of current condition used by females to adjust reproductive investment. Oecologia, 149(3), 535-542.

This week I will talk about animal that would not immediately come to most people’s minds when discussing elaborate courtship displays. It is the Peacock spider, Maratus volans.

Although male jumping spiders are known for being quite ornamented compared to the female, peacock spiders, which are endemic to Australia, are an exceptional example. When courting, a male peacock spider will display his brightly coloured opisthosomal flaps that usually stay tucked away around its abdomen. This will be waved around in synchrony with a pair of ornamental legs to impress the female.

A study on the courting behaviour of the male peacock spider however, has found that they employ a multi-modal signalling structure i.e. using multiple tactics when trying to impress. In particular the study showed that the males use visual cues and vibratory modalities in their display. As far as visual displays, certain behaviours were observed such as pedipalp flicker, opisthosomal bobbing, 3^rd leg wave, fan dance, fan-flapping, and pre-mount display.

These behaviours can be observed in the accompanying video where we see one of these amazing courtship displays taking place.

References

Girard MB, Kasumovic MM, Elias DO.2011. Multi-Modal Courtship in the Peacock Spider, Maratus volans. PLoS one 6(9): e25390.

Hey everyone

My name is David Clarke and I have decided to make the main topic of my blog sexual selection throughout the animal kingdom.  It will include many facets that include evolution, sexual dimorphism and the variety of mate finding behaviour that is utilised by different species. My plan is to give an example of sexual selection from a different species each week with information taken from the literature.

For this first post I thought, seeing as though this is an evolution class, I would start with an example from back in the Jurassic, which is also an example of a very simple way of attracting females (in animals), showing off your enlarged genitalia. In this instance it is an extinct insect in the order Mecoptera that existed in the late Middle Jurassic.

Scientists discovered the fossils of two, now new, genera of scorpionfly in the Jiulongshan formation at Daohugou village Ningcheng County in Inner Mongolia, China. Through examinations of the specimens they found that, although similar in size to other Mecopterans in the same era, these new specimens, Miriholcorpa forcipata (Figure 1) and Fortiholcorpa paradoxa (Figure 2) had enlarged male genitalia and extremely long and extended terminal abdominal segments.

The scientists proposed an evolutionary scenario in which these abdominal segments were used to intimidate/compete with other males and/or were used to attract females by showing off their large “penis”. Having these large abdominal segments and  enlarged genitalia could be seen to be quite a burden to carry around however as  they were alive for quite a while  it is thought that the sexual selection and display of these characteristics outweighed the possible poor mobility and bulky body plan in the evolutionary process.

Figure 1 - Photograph and line drawing showing abdominal segments on Miriholcorpa forcipata   Figure 2 - Photograph and line drawing showing abdominal segments in Fortiholcorpa paradoxa  References

ANG, Q., SHIH, C. & REN, D. 2013. The Earliest Case of Extreme Sexual Display with Exaggerated Male Organs by Two Middle Jurassic Mecopterans. PloS one, 8, e71378.