Survival is predicted by territorial status but not wing pigmentation in males of a polythorid damselfly, Euthore fasciata (Odonata: Zygoptera: Polythoridae)

Robust male condition must be favored and should be signaled to conspecifics via enhanced aggression and more highly expressed ornamental traits. One way that such robust condition, and thereby the expression of aggression and ornamental traits, can be assessed is via survival. In odonate adults, condition (in the form of lipid reserves, muscle mass and immune ability) has been correlated with the expression of: (a) territorial behavior (as opposed to nonterritorial, satellite behavior), and (b) larger wing pigmentation patterns. In the present work, we investigated these two patterns using adult males of Euthore fasciata in a field study. Males bear black and white pigmented wing patterns and express territorial and nonterritorial behaviors to secure matings. We predicted that, due to their better condition, territorial males should have higher survival and larger pigmented patterns than nonterritorial males, and that larger pigmented patterns would correlate positively with survival. We marked–recaptured males, measured their pigmented patterns and recorded their behavior. Our results indicated that territorial males (n = 12) had a higher survival, but not larger pigmented areas, than nonterritorial males (n = 39), and that there was no significant relationship between wing pigmentation and survival. This result confirms that territorial males are in better condition than nonterritorial males. However, wing pigmentation does not seem to signal such condition to conspecifics although the reduced number of animals may have affected our analysis. Tentatively, the assumed relationship pigmentation/condition cannot be generalized in odonates

The sicker sex: understanding male biases in parasitic infection, resource allocation and fitness.

The "sicker sex" idea summarizes our knowledge of sex biases in parasite burden and immune ability whereby males fare worse than females. The theoretical basis of this is that because males invest more on mating effort than females, the former pay the costs by having a weaker immune system and thus being more susceptible to parasites. Females, conversely, have a greater parental investment. Here we tested the following: a) whether both sexes differ in their ability to defend against parasites using a natural host-parasite system; b) the differences in resource allocation conflict between mating effort and parental investment traits between sexes; and, c) effect of parasitism on survival for both sexes. We used a number of insect damselfly species as study subjects. For (a), we quantified gregarine and mite parasites, and experimentally manipulated gregarine levels in both sexes during adult ontogeny. For (b), first, we manipulated food during adult ontogeny and recorded thoracic fat gain (a proxy of mating effort) and abdominal weight (a proxy of parental investment) in both sexes. Secondly for (b), we manipulated food and gregarine levels in both sexes when adults were about to become sexually mature, and recorded gregarine number. For (c), we infected male and female adults of different ages and measured their survival. Males consistently showed more parasites than females apparently due to an increased resource allocation to fat production in males. Conversely, females invested more on abdominal weight. These differences were independent of how much food/infecting parasites were provided. The cost of this was that males had more parasites and reduced survival than females. Our results provide a resource allocation mechanism for understanding sexual differences in parasite defense as well as survival consequences for each sex

Resource allocation in thoracic fat in both sexes.

<p>Predicted thoracic fat content (mg) values of adults according to food treatment, sex and age class triple interaction. Error bars show 95% confidence intervals.</p

Expected survival and sex after infection.

<p>Expected median survival time according to species, sex, infection treatment and age. Black symbols = males, gray symbols = females. Filled symbols = parasite-increased, empty symbols = parasite-control. Error bars show 95% confidence intervals. a) <i>Argia anceps</i>, b) <i>A. extranea</i>, c) <i>Hetaerina americana</i> and d) <i>Protoneura cara</i>.</p

Parasite infection after food stress in both sexes.

<p>Predicted gregarine abundance according to sex and food treatment interaction. Error bars show 95% confidence intervals.</p

Sex biases in parasitism: experimental data.

<p>Predicted gregarine abundance for the experimental study, according to sex, experimental infection and age class. PTM = Parasite-treated males, PCM = Parasite-control males, PTM = Parasite-treated females, PCF = Parasite-control females. Error bars show 95% confidence intervals.</p

Analysis of deviance of expected gregarine abundance according to species identity, food treatment (fed and starved), sex, infection treatment (parasite-treated and parasite-control), thoracic fat content and wing length.

<p>Analysis of deviance of expected gregarine abundance according to species identity, food treatment (fed and starved), sex, infection treatment (parasite-treated and parasite-control), thoracic fat content and wing length.</p

Parasitism rate after experimental infection in both sexes.

<p>Predicted abundance of gregarines according to sex and experimental infection interaction. Error bars show 95% confidence intervals.</p

Sex biases in parasitism: observational gregarine data.

<p>Predicted gregarine abundance for the observational study according to sex, host species and age class third order interaction. Codes for species identity: Aa = <i>Argia anceps</i>, Ae = <i>A. extranea</i>, Ah = <i>A. harknessi</i>, Ap = <i>A. pulla</i>, At = <i>Argia tezpi</i>, Asp = <i>Argia sp.</i>, En = <i>Enallagma novahispaniae</i>, Ha = <i>Hetaerina americana</i>, Pc = <i>Protoneura cara</i>, Ts = <i>Telebasis salva.</i> Error bars depict 95% confidence intervals.</p