Does sexual experience affect the strength of male mate choice for high‐quality females in Drosophila melanogaster?

Although females are traditionally thought of as the choosy sex, there is increasing evidence in many species that males will preferentially court or mate with certain females over others when given a choice. In the fruit fly, Drosophila melanogaster, males discriminate between potential mating partners based on a number of female traits, including species, mating history, age, and condition. Interestingly, many of these male preferences are affected by the male''s previous sexual experiences, such that males increase courtship toward types of females that they have previously mated with and decrease courtship toward types of females that have previously rejected them. D. melanogaster males also show courtship and mating preferences for larger females over smaller females, likely because larger females have higher fecundity. It is unknown, however, whether this preference shows behavioral plasticity based on the male''s sexual history as we see for other male preferences. Here, we manipulate the sexual experience of D. melanogaster males and test whether this manipulation has any effect on the strength of male mate choice for large females. We find that sexually inexperienced males have a robust courtship preference for large females that is unaffected by previous experience mating with, or being rejected by, females of differing sizes. Given that female body size is one of the most common targets of male mate choice across insect species, our experiments with D. melanogaster may provide insight into how these preferences develop and evolve.     

Evolutionary Profile for (Host and Viral) MLKL Indicates Its Activities as a Battlefront for Extensive Counteradaptation

Pathogen infection triggers host innate defenses which may result in the activation of regulated cell death (RCD) pathways such as apoptosis. Given a vital role in immunity, apoptotic effectors are often counteracted by pathogen-encoded antagonists. Mounting evidence indicates that programmed necrosis, which is mediated by the RIPK3/MLKL axis and termed necroptosis, evolved as a countermeasure to pathogen-mediated inhibition of apoptosis. Yet, it is unclear whether components of this emerging RCD pathway display signatures associated with pathogen conflict that are rare in combination but common to key host defense factors, namely, rapid evolution, viral homolog (virolog), and cytokine induction. We leveraged evolutionary sequence analysis that examines rates of amino acid replacement, which revealed: 1) strong and recurrent signatures of positive selection for primate and bat RIPK3 and MLKL, and 2) elevated rates of amino acid substitution on multiple RIPK3/MLKL surfaces suggestive of past antagonism with multiple, distinct pathogen-encoded inhibitors. Furthermore, our phylogenomics analysis across poxvirus genomes illuminated volatile patterns of evolution for a recently described MLKL viral homolog. Specifically, poxviral MLKLs have undergone numerous gene replacements mediated by duplication and deletion events. In addition, MLKL protein expression is stimulated by interferons in human and mouse cells. Thus, MLKL displays all three hallmarks of pivotal immune factors of which only a handful of factors like OAS1 exhibit. These data support the hypothesis that over evolutionary time MLKL functions—which may include execution of necroptosis—have served as a major determinant of infection outcomes despite gene loss in some host genomes.     

Upstream trophic structure modulates downstream community dynamics via resource subsidies

In many natural systems, the physical structure of the landscape dictates the flow of resources. Despite mounting evidence that communities’ dynamics can be indirectly coupled by reciprocal among ecosystem resource flows, our understanding of how directional resource flows might indirectly link biological communities is limited. We here propose that differences in community structure upstream should lead to different downstream dynamics, even in the absence of dispersal of organisms. We report an experimental test of the effect of upstream community structure on downstream community dynamics in a simplified but highly controlled setting, using protist microcosms. We implemented directional flows of resources, without dispersal, from a standard resource pool into upstream communities of contrasting interaction structure and then to further downstream communities of either one or two trophic levels. Our results demonstrate that different types of species interactions in upstream habitats may lead to different population sizes and levels of biomass in these upstream habitats. This, in turn, leads to varying levels of detritus transfer (dead biomass) to the downstream communities, thus influencing their population densities and trophic interactions in predictable ways. Our results suggest that the structure of species interactions in directionally structured ecosystems can be a key mediator of alterations to downstream habitats. Alterations to upstream habitats can thus cascade down to downstream communities, even without dispersal.     

Exploring the relationship between tychoparthenogenesis and inbreeding depression in the Desert Locust,Schistocerca gregaria

Tychoparthenogenesis, a form of asexual reproduction in which a small proportion of unfertilized eggs can hatch spontaneously, could be an intermediate evolutionary link in the transition from sexual to parthenogenetic reproduction. The lower fitness of tychoparthenogenetic offspring could be due to either developmental constraints or to inbreeding depression in more homozygous individuals. We tested the hypothesis that in populations where inbreeding depression has been purged, tychoparthenogenesis may be less costly. To assess this hypothesis, we compared the impact of inbreeding and parthenogenetic treatments on eight life‐history traits (five measuring inbreeding depression and three measuring inbreeding avoidance) in four laboratory populations of the desert locust, Schistocerca gregaria, with contrasted demographic histories. Overall, we found no clear relationship between the population history (illustrated by the levels of genetic diversity or inbreeding) and inbreeding depression, or between inbreeding depression and parthenogenetic capacity. First, there was a general lack of inbreeding depression in every population, except in two populations for two traits. This pattern could not be explained by the purging of inbreeding load in the studied populations. Second, we observed large differences between populations in their capacity to reproduce through tychoparthenogenesis. Only the oldest laboratory population successfully produced parthenogenetic offspring. However, the level of inbreeding depression did not explain the differences in parthenogenetic success between all studied populations. Differences in development constraints may arise driven by random and selective processes between populations.     

Stoichiometry of soil enzyme activity at global scale

Extracellular enzymes are the proximate agents of organic matter decomposition and measures of these activities can be used as indicators of microbial nutrient demand. We conducted a global-scale meta-analysis of the seven-most widely measured soil enzyme activities, using data from 40 ecosystems. The activities of beta-1,4-glucosidase, cellobiohydrolase, beta-1,4-N-acetylglucosaminidase and phosphatase g(-1) soil increased with organic matter concentration; leucine aminopeptidase, phenol oxidase and peroxidase activities showed no relationship. All activities were significantly related to soil pH. Specific activities, i.e. activity g(-1) soil organic matter, also varied in relation to soil pH for all enzymes. Relationships with mean annual temperature (MAT) and precipitation (MAP) were generally weak. For hydrolases, ratios of specific C, N and P acquisition activities converged on 1 : 1 : 1 but across ecosystems, the ratio of C : P acquisition was inversely related to MAP and MAT while the ratio of C : N acquisition increased with MAP. Oxidative activities were more variable than hydrolytic activities and increased with soil pH. Our analyses indicate that the enzymatic potential for hydrolyzing the labile components of soil organic matter is tied to substrate availability, soil pH and the stoichiometry of microbial nutrient demand. The enzymatic potential for oxidizing the recalcitrant fractions of soil organic material, which is a proximate control on soil organic matter accumulation, is most strongly related to soil pH. These trends provide insight into the biogeochemical processes that create global patterns in ecological stoichiometry and organic matter storage.     

Manduca sexta prothoracicotropic hormone: evidence for a role beyond steroidogenesis

Prothoracicotropic hormone (PTTH) is a homodimeric brain peptide hormone that positively regulates the production of ecdysteroids by the prothoracic gland of Lepidoptera and probably other insects. PTTH was first purified from heads of adult domestic silkworms, Bombyx mori. Prothoracic glands of Bombyx and Manduca sexta undergo apoptosis well before the adult stage is reached, raising the recurring question of PTTH function at these later stages. Because Bombyx has been domesticated for thousands of years, the possibility exists that the presence of PTTH in adult animals is an accidental result of domestication for silk production. In contrast, Manduca has been raised in the laboratory for only five or six decades. The present study found that Manduca brains contain PTTH at all stages examined post‐prothoracic gland apoptosis, i.e., pharate adult and adult life, and that PTTH‐dependent changes in protein phosphorylation and protein synthesis were observed in several reproductive and reproduction‐associated organs. The data indicate that PTTH indeed plays a role in non‐steroidogenic tissues and suggest possible future avenues for determining which cellular processes are being so regulated. © 2009 Wiley Periodicals, Inc.     

Are rates of species diversification correlated with rates of morphological evolution?

Some major evolutionary theories predict a relationship between rates of proliferation of new species (species diversification) and rates of morphological divergence between them. However, this relationship has not been rigorously tested using phylogeny-based approaches. Here, we test this relationship with morphological and phylogenetic data from 190 species of plethodontid salamanders. Surprisingly, we find that rates of species diversification and morphological evolution are not significantly correlated, such that rapid diversification can occur with little morphological change, and vice versa. We also find that most clades have undergone remarkably similar patterns of morphological evolution (despite extensive sympatry) and that those relatively novel phenotypes are not associated with rapid diversification. Finally, we find a strong relationship between rates of size and shape evolution, which has not been previously tested.