Bearded ladies

In sexual dimorphic species, it happens that females sometimes have rudimentary male structures, such as ornate markings. These structures are often code for by the same genes in male and females, however in females they incur both social and reproductive costs.  A study looking at Eastern Fence Lizards (Sceloporus undulates), examined the reproductive success of females with and without these structure.

a) males b) ornate female- 'brearded lady' c) standard female

The male Eastern Fence Lizards have bright blue throat marking, which they use when courting females and warding off other males. The females tend to have white throats and bellies, and a general brow colouration, though some females have a blue tinge – ‘bearded ladies’.

In experiments, done by Pennsylvania State University, the effect of being a ‘bearded lady’ was assessed. The team captured and raised lizards in the lab, and then observed mating behaviour. Researches presented males with two females, one with ornate marking, and one without. They found that males preferred female without makings, spending more time on court ship. Ornate females also had a lower reproductive output, and eggs that were laid hatched later then non-ornate females. This showed that ‘Bearded lady’ lizards suffer a cost from their features.

Where there is a cost there must be some benefit, and the exact benefits are not resolved. There a a few postulated benefits, include more aggressive females-due to higher testosterone- which serves which may serve in female-female completion or in predator defence. The trait could be a “snapshot” of a phenotype that is about to be lost from the gene pool.  The reasoning for this trait still waits to be revealed.

Reference: 

Swierk, L, Langkilde, T 2013, ‘Bearded ladies: females suffer fitness consequences when bearing male traits’, The Royal Society, vol.9 no.6.

Isopod morph α, β, ϒ

In the Gulf of California, living on intertidal sponges is a species of isopod Paracerceis sculpta, which displays another type of male polymorphism. Males have ,again, three morphs body types that each has variation in reproductive successes depending on what other type of males are present. Living on or in the sponge, three male morphs maybe present: 

ϒ                             β                                  α
The tree male morph types

Large α males that defend harems, smaller β males that mimic females in appearance and behaviour, and minuscule ϒ males that hide themselves within the sponge with large harems. To understand how male-male-male interactions functions, researches observed and alter male densities and recorded their relative reproductive success. The reproductive capability of each male morph was found to be equal, if isolated with females.  However, depending on what male morphs, as well as the number of females, were present the reproductive success changed.  The researches devised a set of rules for matting success (Table 1).

The researchers, after two years of testing and observation, using genetic marks to trace paternity, found these rules to be effective way to explain the interaction. 

Reference 

Shuster, S & Wade, M 1991, 'Equal mating success among males reproductive strategies in marine isopod', Nature, vol 350, pp.608-610.

An evolutionary game of Rock Papers Scissors.

 Introducing the common side blotched lizard (Uta stansburiana) from the coast range of California. This species has a very cool polymorphism among males. Polymorphism means that different males will have a different colours or body shape/size. In the population of side blotched lizards there are three types of male morphs:

Orange throat males:

 Larger and more aggressive than other male morphs. They can defend large territories and in direct male-male interaction will win. However, Orange males are not very observant of what its females are doing.

Blues throat males:

 Moderate size not as aggressive as orange males. They defend a moderate to small territory. Blue males are well connected and “know” each female in his group.
 Yellow throat males:
 Small, unaggressive and avoiding direct conflict. They do not defend any territory. Yellow males look like females and use this to sneak mates.

 Each one of these male morphs is heritable. The three types of males have their pros and cons, and the interaction of all three plays out in to a dynamic yet stable game of “rock, paper, scissors”. An orange male (rock) by using its superior strength can steals mates from blue males (scissors). However, an orange male will lose to a yellow “sneaker” male (paper), who thanks to the orange males inattention to his female. Yellow males infiltrate orange male’s territory, disguised as a female, and mates with the orange’s females. Yellow (paper) male’s strategy will fail when met by a blue (scissor) male. The blue males, with his smaller group of females which he “knows” individually, is attuned to when a yellow males tries to sneak to mate with his females and is able to scare off the smaller yellow male.

 

 This system was study for six years where researchers observed a fluctuating in the numbers of orange, blue, and yellow males in the population. The population of these lizards neatly demonstrate frequency-dependant selection. That is, as one morph becomes more prevalent it greatly increases the fitness of its counter male, and the counter male will increase its frequency. This new morph prevalence will favour the new morph’s counter male, and so the third morph will become dominate, which in turn will lose to the first morph.
 Even with a game like “rock, paper, scissors”, again we can see that nature thinks of things first.

Reference:
Sinervo, B. & Lively, C.M. 1996, "The rock-paper-scissors game and the evolution of alternative male strategies", Nature, vol. 380, no. 6571, pp. 240-243. 

Battle of the sexes

 In order to understand what we see I thought it important to talk about what drives each sex to do what they do. It may seem that both sexes are working to a similar goal of reproduction, however the reality  is not so simple. Each sex is playing for their interests. Females want reliable good mates and males just wanting to spread their seed as much as possible.
 The first thing to look at what the energy cost are that a female or a male put into making offspring. Females need to produce eggs; eggs take a lot of energy to produce, and a female may only require one mating to fertilize them all. So for a female to produce the most or the best quality offspring she needs to obtain a lot of resources, as sperm is somewhat easy to come by. It is then said that, females are resource limited.
From a male point of view, the production of sperm is "cheap". Males can produce hundreds of thousands of sperm with very little energy cost. A male can produce far more babies at a faster rate than a female can keep up with. That is, one male can knock up more than one female at a time, but a female can only really have one baby every 9 months (in humans). They main thing the male can't find on a Saturday night is someone to take home. The male is therefore female limited.

                                

These differences in needs, females needing resources, males needing females, produce different dispersion patterns of the sexes in the environment. A female’s distribution is determined by resource availability. Whereas, a male's distribution, who need to find mates, is determined on where females are located. This leads to females being the ones choosing mates and males need to find females, initiate courtship, fight over mates.
Women will go to the bar for lady's night where they get free drinks, a resource. This in turn will bring men in to the bar following where the ladies will be.

Welcome

Drosophila in action

Welcome to my Blog, here I plan to look at sexual selection and how/why different animals choose their prospective mates. Looking at the possibly contradictory of needs for males and females when it comes to business time and how that leads to the diversity of behaviors.

My personal interest is the connections and parallels that can be made between other specie's mate choice and how similar/the same humans are, a nice reminder of how not different we are. With this blog I hope to enlighten and bring understand what you see at Gilligans.




Image source:Wikimedia Commons/TheAlphaWolf