Jorge Contreras-Garduño

The lek mating system of Hetaerina damselflies (Insecta: Calopterygidae).

Summary We investigated whether territorial males of Hetaerina damselflies show lekking behaviour using experimental techniques and observations: (i) we altered potential vegetation substrates to determine whether this affected the number of female visitations and matings; (ii) by removing territorial males and allowing other males to occupy the territory, we determined whether females changed their visitation and mating number; (iii) we observed whether vegetation substrates were present and used, and whether lighting conditions affected male territorial behaviour; (iv) we documented female pre- and post-copulatory behaviour to examine whether female choice occurred; and (v) we investigated whether male traits were linked to mating success. Our results revealed that (1) vegetation substrates were rarely found in territories and even when vegetation was present, it did not affect female visitation and mating number; (2) males constantly moved to more illuminated places and females had little opportunity to exert choice due to harassment from males; (3) females oviposited outside territories; and (4) males with larger wing pigmentation and body size obtained a larger mating number because they were more likely to acquire a territory and/or displace other males while in tandem. This is the first documented evidence that odonate males display a lek mating system.

Cost of immune priming within generations: trade-off between infection and reproduction

Immune priming is a new paradigm in innate immunity. However, most studies have focused on the benefits of priming (enhanced survival and parasite clearance after a second challenge), while little attention has been paid to the costs. In this study, both factors were investigated in Anopheles albimanus primed against Plasmodium berghei. As previously observed in other invertebrates, compared to un-primed mosquitoes, those primed better controlled a challenge from the same parasite, and had a higher survival rate. Although there was no difference in the number of oviposited eggs between primed and control females, hatching rate was lower in primed than in control mosquitoes and it was more likely for control females to produce eggs than for primed females. Furthermore, a trade-off between parasite elimination and egg production was observed among primed mosquitoes, as primed females that successfully fought the infection were unable to produce eggs, but primed females that produced eggs were similarly infected as control un-primed ones. These results concord with recent mathematical models suggesting that reproduction affects immune priming outcomes, and may explain why in some species and under some conditions it seems that immune priming is not occurring.

Insect immune priming: ecology and experimental evidences

1. Immune priming refers to improved protection of the host after a second encounter with the same parasite or pathogen. This phenomenon is similar to that of adaptive immunity in vertebrates.

Cross cultural variation in men's preference for sexual dimorphism in women's faces

Both attractiveness judgements and mate preferences vary considerably cross-culturally. We investigated whether mens preference for femininity in womens faces varies between 28 countries with diverse health conditions by analysing responses of 1972 heterosexual participants. Although men in all countries preferred feminized over masculinized female faces, we found substantial differences between countries in the magnitude of mens preferences. Using an average femininity preference for each country, we found mens facial femininity preferences correlated positively with the health of the nation, which explained 50.4% of the variation among countries. The weakest preferences for femininity were found in Nepal and strongest in Japan. As high femininity in women is associated with lower success in competition for resources and lower dominance, it is possible that in harsher environments, men prefer cues to resource holding potential over high fecundity.

Applications of Flow Cytometry to Characterize Bacterial Physiological Responses

Although reports of flow cytometry (FCM) applied to bacterial analysis are increasing, studies of FCM related to human cells still vastly outnumber other reports. However, current advances in FCM combined with a new generation of cellular reporter probes have made this technique suitable for analyzing physiological responses in bacteria. We review how FCM has been applied to characterize distinct physiological conditions in bacteria including responses to antibiotics and other cytotoxic chemicals and physical factors, pathogen-host interactions, cell differentiation during biofilm formation, and the mechanisms governing development pathways such as sporulation. Since FCM is suitable for performing studies at the single-cell level, we describe how this powerful technique has yielded invaluable information about the heterogeneous distribution of differently and even specialized responding cells and how it may help to provide insights about how cell interaction takes place in complex structures, such as those that prevail in bacterial biofilms.

Cross-cultural variation in women's preferences for cues to sex- and stress-hormones in the male face

Women in the UK prefer the faces of men with low levels of the stress hormone cortisol, and the relationship is moderated by the sex hormone testosterone. In a Latvian sample, however, womens preferences were not affected by cortisol, and the interaction with testosterone differed from that of the UK. To further explore cross-cultural variation in preferences for facial cues to sex- and stress-hormones, we tested the preferences of women from 13 countries for facial composites constructed to differ in combinations of the hormones. We found significant relationships between a measure of societal development (the United Nations human development index 2011) and preferences for cues to testosterone in the face, and the interaction between preferences for cues to testosterone and cortisol. We also found a significant relationship between preferences for cues to testosterone and a societal-level measure of parasite stress. We conclude that societal-level ecological factors influence the relative value of traits revealed by combinations of sex- and stress-hormones.

Long-term costs of using heavy shells in terrestrial hermit crabs (Coenobita compressus) and the limits of shell preference: an experimental study

Terrestrial hermit crabs use mollusc shells to protect their soft bodies from predation and desiccation, but their use is costly. The energetic short-term cost of using shells has been demonstrated, yet this could theoretically be overcome by increasing feeding rate or food quality. In the long term, shells have the potential to constrain growth, which may in turn have a negative effect on fitness. Thus crabs should choose the lightest (least expensive to carry) shell amongst those of a size that permit growth. Since in nature lighter shells are also thinner-walled, these may provide insufficient protection from predation or desiccation, facing the crabs with a trade-off between protection and growth. This potential trade-off was investigated in the terrestrial hermit crab Coenobita compressus. Crabs were individually maintained in captivity for a variable period of between 1 and 7 months, during which light or heavy replicates of the preferred shell were available. In a second experiment, crabs were given a choice between a thick (and heavy) or a thin (and light) shell. In addition, the resistance and water retention capacity of thin and thick shells was compared. As predicted, crab growth was negatively correlated with the weight of the shell used, but crabs rejected the thin (light) shells. Thin shells were more likely to break when crabs used the normal ‘rolling’ behaviour in response to perceived threats. In addition, thin shells lost water at a faster rate than thick ones. Since two putative functions of shell use in terrestrial hermit crabs are protection against predation and against desiccation, it is inferred that the preference for shells of intermediate weight in C. compressus results from a balance between the need to grow and the cost of carrying a brittle shell that is not sufficiently water tight.

Juvenile hormone favors sexually-selected traits but impairs fat reserves and abdomen mass in males and females

The physiological mechanism underlying resource allocation in sexual selection studies has been little studied. One candidate is hormones as these favor resource allocation to reproductive traits but impair survival due to a resource over-expenditure directed to the former traits. We have investigated whether a juvenile hormone analog (JHa, methoprene) administrated topically is involved in the resource allocation to wing pigmentation (an ornamental trait), fat reserves and flight muscle mass in both sexes of Calopteryx haemorrhoidalis and C. virgo. We also investigated the possible negative effect of such implementation on abdomen mass (an indirect measure of egg production) and field-based survival in adult males of C. haemorrhoidalis and C. splendens. We found that males and females treated with JHa, against a control group, developed higher wing pigmentation and showed reduced fat reserves but had no change in muscle mass. In females, JHa decreased abdominal weight (an indicator of fecundity) and in males, survival was impaired only in C. splendens. These results support the idea that JH induces resource allocation to wing pigmentation, a sexually selected trait in both sexes. Thus, this study suggests that the action of JH could be a mechanistic link between ornaments and physiological condition in both males and females.

Spatial and temporal population differences in male density and condition in the American rubyspot, Hetaerina americana (Insecta: Calopterygidae)

Increased resource availability should favor higher animal density. It may also affect sex ratio, the male condition, and mating competition over access to females, although the direction of these variables is not straightforward to predict. Using a non-experimental approach, we carried out preliminary research using the territorial American rubyspot (Hetaerina americana) by comparing two spatially separated populations and the same population in two different seasons (each comparison with varying population densities). We first compared the sex ratio by counting males (using two categories, territorial and non-territorial) and females; relative foraging time (as an indicator of how much feeding resources each site provides); wing spot size (a sexual ornament), body size and immune melanization response (these two variables were used to assess male condition); and fighting time and contest number (to assess competition). For the seasonal comparison we used a third population in which we only compared male spot size and two indicators of condition and immune response, phenoloxidase (PO) and nitric oxide (NO) activity. The high-density population had higher values of non-territorial males (but similar sex ratio), relative foraging time, contest time and number, wing spot (but similar body size) and melanization response than the low-density population. According to season, at high density, males had higher values of wing spots, PO, and NO. Our results suggest that in a population where animals have more dietary resources, males reach a better condition despite the competition being more intense.

Ecological distribution and niche segregation of sibling species: the case of bean beetles, Acanthoscelides obtectus Say and A. obvelatus Bridwell

Abstract 1. Molecular techniques have greatly added to the number of known sympatric cryptic species in insects. Ecological differences between these newly distinguished species are little explored, but niches often appear to overlap strongly. These cases are good models for exploring new ideas about species coexistence and community structure.