Front dynamics in fractional-order epidemic models

A number of recent studies suggest that human and animal mobility patterns exhibit scale-free, Lévy-flight dynamics. However, current reaction-diffusion epidemics models do not account for the superdiffusive spread of modern epidemics due to Lévy flights. We have developed a SIR model to simulate the spatial spread of a hypothetical epidemic driven by long-range displacements in the infective and susceptible populations. The model has been obtained by replacing the second-order diffusion operator by a fractional-order operator. Theoretical developments and numerical simulations show that fractional-order diffusion leads to an exponential acceleration of the epidemic's front and a power-law decay of the front's leading tail. Our results indicate the potential of fractional-order reaction-diffusion models to represent modern epidemics.     

Lévy Flights in Dobe Ju/’hoansi Foraging Patterns

We analyzed data on Ju/’hoansi hunter–gatherer foraging patterns and found that their movements between residence camps can be modeled as a Lévy flight. The step lengths of their movements scale as a power law with an exponent μ = 1.97. Their wait times (residence times) at the camps also scale as a power law (μ = 1.45). A Lévy flight with step lengths μ = 2 is an optimal search pattern for scarce, randomly located targets; thus, the Ju/’hoansi foraging pattern may approach an optimal search in this area of sparse plant and animal resources. These findings affect the application of optimal foraging theory to humans in anthropology and archaeology because they alter the way in which search and travel times should be quantified. These results may also carry implications for the study of other patterns of human movement, such as demic diffusion and migration.

Microsatellite markers developed using a next‐generation sequencing technique for Neotrogla spp. (Psocodea: Prionoglarididae), cave dwelling insects with sex‐reversed genitalia

The genus Neotrogla (Psocodea: Prinoglarididae) comprises four named species from Brazil. Females of this cave‐dwelling insect are characterized by a conspicuous penis‐like intromittent organ, termed a gynosome, which is inserted into the vagina‐like male genitalia during copulation. Another evolutionarily novel structure, the spermathecal plate, enables a female to simultaneously store two freshly deposited spermatophores (consisting of sperm and possibly nutritious substances) in her sperm storage organ (spermatheca). It is unknown whether the two spermatophores are derived from two different males. To investigate the mating ecology and population genetic structures of these insects with sex‐reversed genitalia, 16 novel highly polymorphic microsatellite loci were isolated and characterized based on ~2,275 Mbp genomic sequences from an undescribed Neotrogla species. Our first screening detected 99,888 candidate loci. Similar to other hemipteroid insects studied thus far, AAT motif microsatellites were conspicuously dominant. We further screened 99 sequences, for which 50 pairs of polymerase chain reaction primers were successfully designed. Sixteen of these primers successfully amplified products of the expected size in the 11 Neotrogla sp. individuals collected from two caves. The number of alleles per loci varied from two to nine, with no significant deviation from the Hardy–Weinberg equilibrium in either population. Although the caves sampled were only approximately 1 km apart, significant genetic differentiation was detected between the two populations. In total, 13, 12, 13 and 11 loci were cross‐amplified in N. aurora, N. brasiliensis, N. curvata and N. truncata, respectively, indicating the applicability of these microsatellite loci for metapopulation genetic studies in multiple Neotrogla species.     

High opportunity for postcopulatory sexual selection under field conditions

In polygamous systems, male fitness is determined not only by mating success but also by fertilization success. Despite the growing interest over the past several decades in postcopulatory sexual selection, its relative importance compared to precopulatory sexual selection remains a subject of debate. Here, we use extensive behavioral observations of a seminatural population of Hawaiian swordtail crickets, Laupala cerasina, and molecular paternity assignment to measure the opportunities for pre‐ and postcopulatory selection. Because postcopulatory selection has the potential to operate at multiple stages, we also separately attribute its effects to factors specific to mating events versus factors specific to males. We find that variance in postcopulatory success is over four times as great as variance in precopulatory success, with most of it unexplained by male mating order or the number of nuptial gifts given. Surprisingly, we also find that male singing effort is under postcopulatory selection, suggesting that males who sing more frequently also have more competitive ejaculates. Our results are consistent with the hypothesis that high polyandry levels promote greater relative postcopulatory selection. They also highlight the need for detailed behavioral observations under conditions as natural as possible when measuring mating and reproductive success.     

Sexual isolation promotes divergence between parapatric lake and stream stickleback

Speciation can be initiated by adaptive divergence between populations in ecologically different habitats, but how sexually based reproductive barriers contribute to this process is less well understood. We here test for sexual isolation between ecotypes of threespine stickleback fish residing in adjacent lake and stream habitats in the Lake Constance basin, Central Europe. Mating trials exposing females to pairings of territorial lake and stream males in outdoor mesocosms allowing for natural reproductive behaviour reveal that mating occurs preferentially between partners of the same ecotype. Compared to random mating, this sexual barrier reduces gene flow between the ecotypes by some 36%. This relatively modest strength of sexual isolation is surprising because comparing the males between the two ecotypes shows striking differentiation in traits generally considered relevant to reproductive behaviour (body size, breeding coloration, nest size). Analysing size differences among the individuals in the mating trials further indicates that assortative mating is not related to ecotype differences in body size. Overall, we demonstrate that sexually based reproductive isolation promotes divergence in lake–stream stickleback along with other known reproductive barriers, but we also caution against inferring strong sexual isolation from the observation of strong population divergence in sexually relevant traits.     

Phospholipid composition and pheromonal activity of nuptial secretion of the male German cockroach, Blattella germanica

As a part of the sequential courtship behavior of the German cockroach, Blattella germanica, females feed on the nuptial secretion from the male tergal glands. The pheromonal secretion, consisting mainly of oligosaccharides and phospholipids, strongly elicits a feeding response in virgin females. The phospholipids were composed of phosphatidylethanolamine and phosphatidylcholine. Their fatty acid compositions were determined by chromatographic and enzymatic methods. Although an authentic blend of phospholipids (1,2-dioleoylphosphatidylethanolamine and 1,2-dioleoylphosphatidylcholine) showed a marginal phagostimulant activity, addition of the blend to an authentic blend of oligosaccharides (maltose and maltotriose) strongly enhanced the activity to nearly the level of the crude extract. These results indicate that the nuptial feeding behavior is elicited by a synergistic action between phospholipids and oligosaccharides.     

Fitness advantage from nuptial gifts in female fireflies

Abstract 1. In many insects, males provide nuptial gifts to females in the form of spermatophores, sperm-containing structures produced by male accessory glands.
2. The work reported here examined the influence of both spermatophore number and spermatophore size on female reproductive output in two related firefly beetles, Photinus ignitus and Ellychnia corrusca (Coleoptera: Lampyridae). Based on differences in adult diet, male spermatophores were predicted to increase female reproductive output to a greater extent in P. ignitus than in E. corrusca .
3. Female fecundity was significantly higher in triply mated females than in singly mated females in both species, with no difference between mating treatments in female lifespan or egg hatching success. No effects of second male spermatophore size on fecundity, lifespan, or egg hatching success were detected in either species.
4. These results suggest a direct fitness advantage from multiple mating for females in both species, although enhanced fecundity may be due either to allocation of spermatophore nutrients to eggs or to other substances transferred within the spermatophore acting as oviposition stimulants.     

Ejaculate expenditures of male crickets in response to varying risk and intensity of sperm competition: not all species play games

Costs incurred in the manufacture of ejaculates may constrainthe number of sperm that males can produce, so males shouldshow some economy in their allocation of sperm across multiplematings. In species in which females mate with multiple malesand are capable of storing sperm for extended periods, spermallocation of males should be tailored to the risk of spermcompetition. Recent game theory predicts that males shouldtransfer the least sperm when there are no other rivals, andthe most sperm when only one other rival is likely to inseminatethe female. However, as the numbers of competitors increasesbeyond two, the models predict a corresponding decrease in ejaculate expenditure. We tested these predictions in three cricket species, Gryllodes sigillatus, Gryllus veletis, and Gryllus texensis, assessing the sperm allocation of males held under three levelsof apparent interrival competition: no rivals, one rival andsix rivals. Sperm allocation of G. veletis varied accordingto theory: males increased their sperm allocation with an increasedrisk of sperm competition (no rivals vs. one), but decreasedtheir allocation with an increased intensity of sperm competition(one rival vs. six). Sperm allocation of male G. texensis showedno significant response to the density of rivals, and spermallocation in G. sigillatus was influenced by an unexpectedinteraction between treatment density and the order in whichmales experienced the three treatments. The observed interspecificvariation in facultative sperm allocation may be due to interspecificdifferences in population density, rearing environment, orfemale mating behavior.     

昆虫性选择行为研究进展

本文综述了昆虫的各种性选择行为,包括与个体大小有关的性选择行为、与鸣声有关的性选择行为、与“婚礼食物”有关的性选择行为以及精子竞争等。     

Nuptial feeding by male bushcrickets: an indicator of male quality?

Male bushcrickets transfer a spermatophore at mating that consistsof a sperm-containing ampulla and a product of the accessoryglands, the spermatophylax, that is consumed by the female duringinsemination. Male Requena verticalis produce functionally differentspermatophores depending on the availability of sexually receptivefemales. They will maintain high mating frequency by providinga gift sufficient to ensure sperm transfer, or will invest parentallyin females when their mating frequency is low. We examined therelationship between male quality and nuptial feeding underconditions where males invest in ejaculate protection or inparental investment. When investing in ejaculate protection,males reduced the quality of the spermatophylax meal by reducingboth the concentration of protein and the absolute amount ofprotein it contained. There was no relationship between malephenotype and gift size or quality. Moreover, we could findno evidence for the recently advanced hypothesis that femalescan exercise mate choice by interfering with insemination. However,when males were investing parentally, we found a positive associationbetween spermatophylax size and male size, but no relationshipbetween protein content and male size. Males with high levels offluctuating asymmetry invested more heavily in the nutritionalcontent of their spermatophylaxes than did symmetrical males.Thus, male quality does influence nuptial feeding, but in amanner predicted by a model of indirect fitness benefits frommate choice.