Agonistic Displays and the Benefits of Fighting in the Field Cricket, Gryllus bimaculatus

Fighting is often composed of discrete agonistic displays. Few studies have partitioned fighting behavior into its component agonistic displays and evaluated the relationships between the frequency of the displays and the potential benefits of fighting, particularly mating success. In this study, we quantified the frequency of male field cricket, Gryllus bimaculatus, agonistic displays. The displays were quantified under three social environments which varied in the potential benefits of fighting: males with other males only, males with other males and female scents, and males with other males and females. We found that (1) the presence of females elicited an increase in agonistic displays characteristic of intermediate levels of escalation, (2) female scents did not produce a similar increase in the frequency of agonistic displays, and (3) in the presence of females, the frequency of agonistic displays was positively correlated with mating success. Aggressive stridulation, an energetically low-cost display, was more strongly associated with mating success than were more costly displays. The results are discussed in the context of the evolutionary theory of aggression and in the context of cricket mating systems.     

Sexual conflict over mating in a spider: increased fecundity does not compensate for the costs of polyandry

Female multiple mating (polyandry) is a widespread but costly behavior that remains poorly understood. Polyandry may arise when whatever benefits females accrue from multiple mating outweigh the costs, or males manipulate females against the females' best interests. In a polyandrous spider Stegodyphus lineatus females may mate with up to five males, but behave aggressively toward additional males after the first mating. Female aggressiveness may act to select for better quality males. Alternatively, females may try to avoid superfluous matings. To test these alternatives, we allocated females into single-mating (SM) and double-mating treatments. Double-mated females either accepted (DM) or rejected (RE) the second male. DM females laid more eggs, but did not produce more offspring than SM and RE females. Offspring of DM females were smaller at dispersal than offspring of SM and RE females. Also, nest failure was significantly more common in DM females. Paternal variables did not influence female reproductive success, whereas maternal body condition explained much of the variation. We show that polyandry is costly for females despite the production of larger clutches and suggest that multiple mating results from male manipulation of female remating behavior.     

Spatial density patterns of herbivore response to seasonal dynamics in the tropical deciduous forest of central India

Resource dynamism in seasonal forests leads ungulates to differential habitat preference; hence, their distribution aligns with environmental covariates across spatial and temporal scales. Seasonal patterns of four species of ungulates, namely sambar, chital, nilgai, and wild pig, were investigated and identified as the environmental variables driving the density gradient across two seasons, summer and winter, in the tropical dry deciduous forest of Panna Tiger Reserve, central India. Distance sampling data were analyzed using density surface modeling for ungulates with a survey effort of 518 km in winter and 356 km in summer in a generalized additive modeling framework. We found that season significantly affected the spatial densities of all ungulates, with sambar, chital, and nilgai congregating in summer and wild pig in winter. All ungulates showed a clear seasonal shift to the valley in summer and preferred plateaus in winter. The spatially explicit map outputs draw attention to the seasonal hot spots for ungulates abundance and the species and season-specific roles of environment variables in defining their distribution. These results provide a scientific basis for direct conservation efforts to the spatially prioritized habitats for cost-effective management interventions.     

Male size does not affect the strength of male mate choice for high-quality females in Drosophila melanogaster

Theory predicts that the strength of male mate choice should vary depending on male quality when higher-quality males receive greater fitness benefits from being choosy. This pattern extends to differences in male body size, with larger males often having stronger pre- and post-copulatory preferences than smaller males. We sought to determine whether large males and small males differ in the strength (or direction) of their preference for large, high-fecundity females using the fruit fly, Drosophila melanogaster. We measured male courtship preferences and mating duration to show that male body size had no impact on the strength of male mate choice; all males, regardless of their size, had equally strong preferences for large females. To understand the selective pressures shaping male mate choice in males of different sizes, we also measured the fitness benefits associated with preferring large females for both large and small males. Male body size did not affect the benefits that males received: large and small males were equally successful at mating with large females, received the same direct fitness benefits from mating with large females, and showed similar competitive fertilization success with large females. These findings provide insight into why the strength of male mate choice was not affected by male body size in this system. Our study highlights the importance of evaluating the benefits and costs of male mate choice across multiple males to predict when differences in male mate choice should occur.     

Natural variation in the sexually selected feather ornaments of crested auklets (Aethia cristatella) does not predict future survival

We evaluated whether sexually selected crest and auricular plumefeather ornaments of crested auklet (Aethia cristatella) adultscovaried with individual local survival over 11 years (1991–2001).Crested auklets (n = 364 total) were captured near breedingsites, marked with color rings, and local survival estimateswere based on color ring resightings at a breeding colony. Survivalestimates and relationships among local survival and crest length,auricular plume length, mass and tarsus were evaluated usingthe program MARK. The best models included four groups, definedby sex and ease of resighting, that differed in resighting rate(p) but not local survival rate (). This model structure effectivelyexplained sources of variation in local survival and resightabilityamong individuals. The best fitting model showed local survivalrate varying annually, while accounting for differences in resightabilityof marked individuals between the sexes and groups ([t], p[sex*easeof resighting]). Annual local survival varied from 0.940 ±0.029 (SE) in 1993–1994 to 0.767 ± 0.034 in 1997–1998and averaged 0.859 ± 0.019. We found no evidence thatcrested auklet local survival covaried with continuous variationin individuals' ornaments. Simulations indicated that our dataset was sufficient to detect a relationship between local survivaland a covariate that equaled or exceeded a range of 8%. Theimplications for competing sexual selection mechanisms of empiricallymeasured survival–ornament relationships are controversial,but our study emphasizes that survival estimates for such investigationsmust control for confounding factors such as resighting rateas well as have sufficient statistical power and time scaleto be biologically meaningful. Our results are most consistentwith the idea that the conspicuous variation in crested auklet'sshowy ornaments is arbitrary with respect to individual viabilityas quantified by their long-term survival.     

Sexual selection did not contribute to the evolution of male lifespan under curtailed age at reproduction in a seed beetle

1. Sexual selection is a powerful evolutionary force that is hypothesised to play an important role in the evolution of lifespan. Here we test for the potential contribution of sexual selection to the rapid evolution of male lifespan in replicated laboratory populations of the seed beetle, Callosobruchus maculatus. 2. For 35 generations, newly hatched virgin male beetles from eight different populations were allowed to mate for 24 h and then discarded. Sexual selection was removed in half of these populations by enforcing random monogamy. 3. Classic theory predicts that because of sexual competition, males from sexually selected lines would have higher age‐specific mortality rates and shorter lifespan than males from monogamous lines. 4. Alternatively, condition‐dependent sexual selection may also favour genes that have positive pleiotropic effects on lifespan and ageing. 5. Males from all eight populations evolved shorter lifespans compared with the source population. However, there was no difference in lifespan between males from populations with or without sexual selection. Thus, sexual selection did not contribute to the evolution of male lifespan despite the fact that such evolution did occur in our study populations.     

Carry‐over effects of conditions at the wintering grounds on breeding plumage signals in a migratory bird: roles of phenotypic plasticity and selection

To understand the consequences of ever‐changing environment on the dynamics of phenotypic traits, distinguishing between selection processes and individual plasticity is crucial. We examined individual consistency/plasticity in several male secondary sexual traits expressed during the breeding season (white wing and forehead patch size, UV reflectance of white wing patch and dorsal melanin coloration) in a migratory pied flycatcher (Ficedula hypoleuca) population over an 11‐year period. Furthermore, we studied carry‐over effects of three environmental variables (NAO, a climatic index; NDVI, a vegetation index; and rainfall) at the wintering grounds (during prebreeding moult) on the expression of these breeding plumage traits of pied flycatcher males at individual and population levels. Whereas NAO correlates negatively with moisture in West Africa, NDVI correlates positively with primary production. Forehead patch size and melanin coloration were highly consistent within individuals among years, whereas the consistency of the other two traits was moderate. Wing patch size decreased with higher NAO and increased with higher rainfall and NDVI at the individual level. Interestingly, small‐patched males suffered lower survival during high NAO winters than large‐patched males, and vice versa during low NAO winters. These counteracting processes meant that the individual‐level change was masked at the population level where no relationship was found. Our results provide a good example of how variation in the phenotypic composition of a natural population can be a result of both environment‐dependent individual plasticity and short‐term microevolution. Moreover, when plasticity and viability selection operate simultaneously, their impacts on population composition may not be evident.