DR. AMANDA  WHISPELL

What is the purpose of the bright coloration exhibited by bright-phase males, and is it an honest signal?

For my doctoral research, I performed extensive field work where I made behavioural observations of Argia apicalis males and females, to document how individuals interact both intra- and intersexually.  I documented all mating events (ME) - a term I use to refer to the collective activities that occur from initial tandem formation between a male and female, through copulation, oviposition, and the final release of the female - as well as any color changes (from bright-phase (BP) to dark-phase (DP)) exhibited by both males and blue-form females in response to low temperatures and MEs.

While this research has shown that the DP coloration is significantly correlated with mating-associated behaviors, and has given good indications regarding anti-predatory benefits that are conferred by the color change, it has left me wondering about the benefits of BP coloration.  When male A. apicalis are in BP, and are defending territories, they often perch on the ground - along dirt paths, on rocks, or on logs.  The bright blue coloration is not only highly conspicuous in the visible spectrum when against a dull, solid background, but males also reflect in the near UV when in BP.  This highly visual signal is not only detectable by conspecifics, but also by any eavesdropping predators that have similar visual competencies.  There must be an evolutionary benefit to being bright blue, otherwise one would expect natural selection to nullify this signal in lieu of more cryptic coloration.  

What is the function?

I would like to analyze whether males are awarded any advantages from the BP coloration, perhaps in increased immunity against pathogens, and/or increased ability to hold a territory and gain more mating opportunities, etc.

Is it an honest signal?

In order for the brightness to be an honest signal, there would have to be some variation in the overall ‘blueness’ (hue, brightness, saturation, area of thorax, UV reflectance) between males, and it would have to be conveying some information about the male’s resource holding potential.  As it seems that males are not holding territories that provide females with greater access to oviposition sites (their territories are often quite far from the water’s edge), it stands to reason that the ‘blueness’ must be, in some way, a representation of his overall health, his superior genes, or perhaps his ability to protect the female from predation during tandem oviposition. 

I would like to test whether brighter/bluer males are in any way healthier:

• Do they have greater fat reserves

• Do they have better genes, perhaps correlating to increased pathogen resistance

How is the evolution of a secondary sexual trait affected by sexual and natural selection?

Numerous studies have shown that the presence of secondary sexual traits, such as the bright coloration depicted by A. apicalis males for example, have been targeted by inter- and/or intrasexual selection, and may have evolved as the result of female choice or inter-male competition for territories and mating opportunities, or both.  These secondary sexual traits are generally thought to act as signals to help attract mates and defend territories via the transmission of information about an individual’s quality or fitness.  These traits, however, are not targeted by sexual selection alone, but by natural selection as well.  The interaction between natural selection and sexual selection acting on the same trait often result in a compromise between being conspicuous to potential mates, and inconspicuous to potential predators, or alternatively result in speciation.

As part of my PhD dissertation, I performed a predator choice experiment that has indicated that some predators do predate on significantly more BP, than DP, A. apicalis males, when given the choice between both.  I would next like to look at the sexual selection side of the question, and determine how successful bright males are in defending territories and accruing reproductive success.  Given that female odonates have the capability to store sperm, the incidence of a ME event alone is not enough evidence to determine reproductive success for a male, thus the opportunity to genetically analyze the endophytically oviposited eggs for paternity would yield more information than mating success alone.  The opportunity to determine how successful males are at removing the previously deposited sperm of prior mates would also provide information regarding the efficacy of sperm competition in this species.