Gustavo S. Requena

Conditional male dimorphism and alternative reproductive tactics in a Neotropical arachnid (Opiliones)

In arthropods, most cases of morphological dimorphism within males are the result of a conditional evolutionarily stable strategy (ESS) with status-dependent tactics. In conditionally male-dimorphic species, the status’ distributions of male morphs often overlap, and the environmentally cued threshold model (ET) states that the degree of overlap depends on the genetic variation in the distribution of the switchpoints that determine which morph is expressed in each value of status. Here we describe male dimorphism and alternative mating behaviors in the harvestman Serracutisoma proximum. Majors express elongated second legs and use them in territorial fights; minors possess short second legs and do not fight, but rather sneak into majors’ territories and copulate with egg-guarding females. The static allometry of second legs reveals that major phenotype expression depends on body size (status), and that the switchpoint underlying the dimorphism presents a large amount of genetic variation in the population, which probably results from weak selective pressure on this trait. With a mark-recapture study, we show that major phenotype expression does not result in survival costs, which is consistent with our hypothesis that there is weak selection on the switchpoint. Finally, we demonstrate that switchpoint is independent of status distribution. In conclusion, our data support the ET model prediction that the genetic correlation between status and switchpoint is low, allowing the status distribution to evolve or to fluctuate seasonally, without any effect on the position of the mean switchpoint.

Efficiency of uniparental male and female care against egg predators in two closely-related syntopic harvestmen

Although the benefits of maternal care have been investigated in many species, the caring role of males in species with exclusive paternal care has received less attention. We experimentally quantified the protective role of paternal care in the harvestman Iporangaia pustulosa. Additionally, we compared the effectiveness of paternal care against predation in this species with a syntopic harvestman with maternal care, Acutisoma proximum. We demonstrated that nearly one-third of the unprotected Iporangaia clutches disappeared entirely in 12 days, while the other two-thirds suffered a mean reduction of 55% in egg number. Conversely, 50% of the control clutches did not suffer any reduction, and only one was entirely consumed by predators. We also demonstrated that the mucus coat that covers Iporangaia clutches has an important deterrent role against predation by conspecifics: 58.3% of the clutches without mucus were attacked and three of them were entirely consumed, whereas only three clutches with mucus were attacked, suffering a reduction of up to three eggs. Iporangaia males were as efficient as Acutisoma females in protecting eggs. However, unattended Acutisoma eggs were attacked 20% more frequently than unattended Iporangaia eggs. Unattended Iporangaia eggs are protected by a mucus coat that prevents or decreases predation rate, whereas Acutisoma eggs are more susceptible to predation, probably because they lack this mucus coat. Thus, besides the fact that Iporangaia males efficiently protect the offspring against egg predators, females also contribute to egg protection by providing a mucus coat that deters egg predators.

Paternal Care Decreases Foraging Activity and Body Condition, but Does Not Impose Survival Costs to Caring Males in a Neotropical Arachnid

Exclusive paternal care is the rarest form of parental investment in nature and theory predicts that the maintenance of this behavior depends on the balance between costs and benefits to males. Our goal was to assess costs of paternal care in the harvestman Iporangaia pustulosa, for which the benefits of this behavior in terms of egg survival have already been demonstrated. We evaluated energetic costs and mortality risks associated to paternal egg-guarding in the field. We quantified foraging activity of males and estimated how their body condition is influenced by the duration of the caring period. Additionally, we conducted a one-year capture-mark-recapture study and estimated apparent survival probabilities of caring and non-caring males to assess potential survival costs of paternal care. Our results indicate that caring males forage less frequently than non-caring individuals (males and females) and that their body condition deteriorates over the course of the caring period. Thus, males willing to guard eggs may provide to females a fitness-enhancing gift of cost-free care of their offspring. Caring males, however, did not show lower survival probabilities when compared to both non-caring males and females. Reduction in mortality risks as a result of remaining stationary, combined with the benefits of improving egg survival, may have played an important and previously unsuspected role favoring the evolution of paternal care. Moreover, males exhibiting paternal care could also provide an honest signal of their quality as offspring defenders, and thus female preference for caring males could be responsible for maintaining the trait.

Paternal Care and Sexual Selection in Arthropods

Abstract Exclusive paternal care is probably the rarest form of post-zygotic parental investment in nature. In arthropods, this behavior has independently evolved in 15 lineages, including approximately 1500 species. Here, we review the theoretical background for the evolution of parental investment and sex roles, contrasting classical views with the most recent mathematical models. Then, we introduce cases of exclusive paternal care in arthropods and explore empirical information, focusing on the costs and benefits of male egg guarding and the possible role of paternal care in male attractiveness and sex role reversal. Finally, we analyze the possible effects of temperature and rainfall on several ecological aspects that are likely to influence the evolution and maintenance of paternal care, and also derive specific macroecological predictions to be tested in future studies.

First cases of exclusive paternal care in stink bugs (Hemiptera: Pentatomidae)

We describe paternal care in two pentatomid bugs, Lopadusa (Lopadusa) augur Stal, 1860 and Edessa nigropunctata Berg, 1884. Field and laboratory observations showed that males remain with their eggs and early hatched nymphs, while females abandon the eggs after oviposition. Guarding males defensive behaviors towards their clutches were similar to those described for guarding females of pentatomids. Since there is no detailed information on the internal phylogeny of Pentatomidae, it is not possible to make a robust inference on whether paternal care in L. augur and E. nigropunctata has arisen independently or not. If the latter, the two new cases of paternal care we describe here represent the fifth event of independent evolution of this rare behavioral trait in Heteroptera.

Costs and benefits of temporary egg desertion in a rocky shore frog with male-only care

Egg attendance imposes costs on parents, including decreased food intake and increased mortality risks. By concentrating parental activities when egg predation is greater and abiotic conditions are less stressful, parents may decrease these costs. Here, we quantify the costs and benefits of temporary egg desertion in the frog Thoropa taophora, whose males care for eggs on rocky shores. We tested hypotheses on the effect of the period of the day (day vs. night) and breeding site (exposed vs. protected from sunlight) on the frequency of temporary desertion, water loss, and egg predation. Using naturalistic observations, we show that parental males deserted their clutches more often during daytime and in exposed sites. Using a field experiment with agar models simulating adult males, we show that water loss was greater during daytime and in exposed sites. Finally, using field observations and a male removal experiment, we show that male presence improves egg survival and that egg predation was higher during the night, with no effect of breeding site. Because the main egg predators are conspecifics, which are mostly inactive when parental males are not attending their clutches, the costs of temporary desertion in terms of egg loss are relatively low when compared with the benefits related to decreased exposure of parental males to stressful abiotic conditions. In conclusion, we predict that temporary offspring desertion should be found especially among ectotherms, when periods of harsher environmental abiotic conditions for the parents are coincident with periods of low offspring demand for protection against predators.Significance StatementTo take care of eggs is costly for the parents because they are exposed to predators or stressful environmental conditions. In order to avoid these costs, parents may leave the eggs temporarily unattended. Although temporary egg desertion has been reported for many species, the selective forces favoring its evolution are still poorly understood. Here, we investigated the costs and benefits of temporary egg desertion in a frog whose males care for eggs on rocky shores, an extreme environment for animals with permeable skin. Our findings lead us to conclude that temporary egg desertion should evolve when periods of harsher environmental conditions for the parents are coincident with periods of low offspring demand for protection against predators.

Chemical communication in the gregarious psocid Cerastipsocus sivorii (Psocoptera: Psocidae).

The objectives of this study were: (1) to test the existence of an aggregation pheromone in the gregarious psocid Cerastipsocus sivorii; (2) to compare the attractiveness of odors from different aggregations; (3) to test whether nymphs are able to chemically recognize damage-released alarm signals. In a choice experiment conducted in the laboratory, we showed that psocids are able to detect chemical cues from groups of conspecifics. Laboratory experiments also showed that nymphs are capable of chemically recognizing the aggregations where they came from. Finally, in a field experiment, most aggregations dispersed when exposed to the body fluids of a crushed conspecific, but no aggregations dispersed upon exposure to a crushed termite. The implications of these results for the evolution of sociality in psocopterans are discussed.