Are local plague endemicity and ecological characteristics of vectors and reservoirs related? A case study in north-east Tanzania

The pattern of plague endemicity in Tanzania is characterized by continuous re-appearance of the disease in some locations,while in other neighbouring villages the disease has never or seldom been observed.To understand the reasons for this pattern,we studied small mammal and flea species composition,diversity and relative abundances in two plague-endemic and two plague-free locations.We asked(a)whether fleas more abundant in plague-endemic locations differ in their characteristic abundance and the degree of their host specificity from fleas more abundant in plague-free locations and(b)whether hosts most abundant in plague-endemic locations differ in the diversity of their flea assemblages from hosts most abundant in plague-free locations.We characterized(a)each host species by species richness and degree of taxonomic relatedness of its flea assemblages and(b)each flea species by its mean abundance and size,and degree of taxonomic relatedness of its host spectrum and compared their relative abundances between locations.No significant difference between plague-endemic and plague-free locations in either host density or any variable related to flea abundance or diversity was found.However,there was marginally significant effect of taxonomic distinctness of a flea assemblage harboured by a host on its probability to be more abundant in either plague-endemic or plague-free locations.Furthermore,hosts more abundant in plague-endemic locations tended to harbour closely-related fleas.Finally,while opportunistic and specialist fleas were equally distributed in both sets of locations,fleas exploiting distantly-related hosts were found mainly in plague-free locations during the rainy season.We suggest that the observed patterns might arise due to seasonal and spatial differences in local microclimatic conditions and landscape connectivity.

Phylogeography of the common hamster(Cricetus cricetus):paleoclimatic reconstructions of Late Pleistocene colonization

INTRODUCTION Anthropogenic activities and associated factors such as climate change and habitat destruction are causing the ongoing sixth mass extinction on Earth,which is a major characteristic of the Anthropocene.Collectively,these factors pose the most serious environmental threat to the existence of civilization because it is irreversible.More than 500 species of mammals were found to be on the brink of extinction and likely to be lost within 20 years(Ceballos et al.2020).One example is the common hamster Cricetus cricetus(Linnaeus,1758).In 2020,this species was classified as Critically Endangered across its global range by the IUCN Red List(Banaszek et al.2020).The protection status of the common hamster was elevated by 4 levels at once—from Least Concern to Critically Endangered.Although the causes behind the dramatic decline of the species are not fully understood,one may suppose it stems from the negative impact of habitat degradation and even climate change(Banaszek et al.2020).

Adaptation to a novel host and performance trade-off in host-generalist and host-specific insect ectoparasites

We investigated the performance trade-offs of fleas(Siphonaptera)while adapting to a novel host using two host generalists(Xenopsylla conformis and Xenopsylla ramesis)and one host specialist(Parapulex chephrenis)maintained on their principal hosts(Meriones crassus for Xenopsylla and Acomys cahirinus for P.chephrenis).We asked whether,over generations,(i)a host generalist may become a specialist by evolving the ability to exploit a novel host and losing the ability to exploit an original host and(ii)a host specialist can become a generalist by evolving the ability to exploit a novel host without losing the ability to exploit an original host.We established an experimental line of each species on a novel host(Acomys russatus for Xenopsylla and M.crassus for P.chephrenis)and maintained this line on this host during 23 generations.We compared reproductive performance of progenitors of each line and their descendants when they exploited either original or novel host in terms of egg number and size,hatching success,offspring production,and offspring size.We found changes in performance over generations in female offspring size only.Xenopsylla conformis demonstrated a tendency to become a host specialist(increased performance on the novel host with a concomitant decreased performance on the original host),whereas P.chephrenis demonstrated a tendency to become a host generalist(increased performance on the novel host without a concomitant decreased performance on the original host).We conclude that the probability of generalist to specialist transition,and vice versa,is context-dependent and varies between species.

Factors shaping life history traits of two proovigenic parasitoids

What shapes the relative investment in reproduction versus survival of organisms is among the key questions in life history.Proovigenic insects mature all their eggs prior to emergence and are short lived,providing a unique opportunity to quantify their lifetime investments in the different functions.We investigated the initial eggloads and longevity of 2 proovigenic parasitoid wasps:Anagrus erythroneurae and Anagrus daanei,(Hymenoptera:Mymaridae)that develop within leafhopper eggs in both agricultural vineyards and natural riparian habitats in Northern California.We collected Vitis spp.leaves containing developing parasitoids from 3 natural sites(Knight Landing,American River and Putah Creek)and 3 agricultural vineyards(Solano Farm,Davis Campus and Village Homes).We recorded eggloads at parasitoid emergence and female parasitoid longevity with or without honey-feeding.Theory predicts that parasitoids from vineyards(where hosts are abundant)would have higher initial eggloads and lower longevity compared with parasitoids from riparian habitats(where hosts are scarce).Although host density and parasitoid eggloads were,indeed,higher in vineyards than in riparian habitats,parasitoid longevity did not follow the predicted pattern.Longevity without feeding differed among field sites,but it was not affected by habitat type(natural vs agricultural),whereas longevity with feeding was not significantly affected by any of the examined factors.Moreover,longevity was positively,rather than negatively,correlated with eggloads at the individual level,even after correcting for parasitoid body size.The combined results suggest a more complex allocation mechanism than initially predicted,and the possibility of variation in host quality that is independent of size.

Seasonal and habitat dependence of fleas parasitic on small mammals in Tanzania

We investigated host and flea species composition across different habitats during dry and rainy seasons in the Western Usambara Mountains in Tanzania.During both seasons,similarity in flea species composition increased with an increase in the similarity in host species composition.Nevertheless,between-season within-habitat as well as within-season between-habitat similarity in host species composition was higher than similarity in flea species composition.Ordination of habitats according to their host and flea species composition demonstrated that the pattern of between-habitat similarity in both host and flea species composition varied seasonally.Despite the relatively rich mammal and flea fauna of the study region,the major contribution to variation in species composition between seasons and among habitats was due to a few species only.Flea assemblages on Lophuromys kilonzoi Verheyen et al.,2007 and Praomys delectorum Thomas,1910 in different habitats were equally similar in either season.In contrast,flea assemblages on Mastomys natalensis(Smith,1834)occurring in different habitats were more similar in the dry than in the rainy season,whereas the opposite was the case for fleas on Grammomys sp.In different hosts,the main differences in species composition of flea assemblages between seasons as well as among habitats were due to different flea species.Although our results support the earlier idea that parasite species composition is determined by both host species composition and habitat properties,the former appears to explain variance in flea species composition between localities in the tropics better than between localities in temperate and arid zones.

Latitudinal gradients in body size and sexual size dimorphism in fleas:males drive Bergmann’s pattern

We tested for the effects of latitude and geographic range size(GRS)on body size,leg length,and sexual size dimorphism(SSD)across 103 species offleas,taking into account phylogenetic between-species relationships.When the data on body size were combined for males and females,the positive correlation between body size and latitude,but not GRS,was revealed.When the analysis was restricted to one sex only,the effect of latitude appeared to be non-significant for females,whereas male body size increased with an increase in latitude.Intraspecific body size variation was not associated with either the latitude or the latitudinal span of the geographic range,independently of which data subset was analyzed.No evidence of association between size-independent tibia length and latitude was found for either females,males,or both sexes combined.The degree of SSD decreased with a decrease in latitude but was not affected by GRS.We conclude that macroecological patterns might be manifested differently in males and females.This should be kept in mind while searching for these patterns.

What do we know about biological nitrogen fixation in insects? Evidence and implications for the insect and the ecosystem

Many insects feed on a low‐nitrogen diet,and the origin of their nitrogen supply is poorly understood.It has been hypothesized that some insects rely on nitrogen‐fixing bacteria(diazotrophs)to supplement their diets.Nitrogen fixation by diazotrophs has been extensively studied and convincingly demonstrated in termites,while evidence for the occurrence and role of nitrogen fixation in the diet of other insects is less conclusive.Here,we summarize the methods to detect nitrogen fixation in insects and review the available evidence for its occurrence(focusing on insects other than termites).We distinguish between three aspects of nitrogen fixation investigations:(i)detecting the presence of potential diazotrophs;(ii)detecting the activity of the nitrogen‐fixing enzyme;and(iii)detecting the assimilation of fixed nitrogen into the insect tissues.We show that although evidence from investigations of the first aspect reveals ample opportunities for interactions with potential diazotrophs in a variety of insects,demonstrations of actual biological nitrogen fixation and the assimilation of fixed nitrogen are restricted to very few insect groups,including wood‐feeding beetles,fruit flies,leafcutter ants,and a wood wasp.We then discuss potential implications for the insect's fitness and for the ecosystem as a whole.We suggest that combining these multiple approaches is crucial for the study of nitrogen fixation in insects,and argue that further demonstrations are desperately needed in order to determine the relative importance of diazotrophs for insect diet and fitness,as well as to evaluate their overall impact on the ecosystem.

Social interactions in striped hyena inferred from camera trap data:is it more social than previously thought?

Understanding the drivers promoting sociality over solitariness in animal species is imperative for predicting future population trends and informing conservation and management.In this study we investigate the social structure of a desert dwelling population of striped hyena Hyaena hyaena.This species is historically regarded as strictly solitary albeit being the least studied of the extant Hyaenids.Accumulating evidence regarding the frequency of social interactions sug-gests a revision of striped hyena social structure is required.We hypothesized that striped hyena has a social structure that is more complex than expected for a strictly solitary species.For that end,we deployed an array of camera-traps in a remote desert region in Israel,and compared observed frequencies of striped hyena co-occurrence against null models to test whether hyena co-occurred more than expected by chance.Seven adults were(re)captured by our camera-traps in 49 different instances over 83 tracking days.Of these,6 exhibited shared space-use around a scarce,isolated perennial water source.Five of them,co-occurred with other hyena(in 3 instan-ces)significantly more frequent than expected by chance(and that timing suggests reproduction is unlikely to be the driving factor).Our findings substantiate evidence of complex social structure in striped hyena,highlight the importance of a scarce resource in space use and sociality,and provide a baseline for future research of striped hyena social structure.We suggest that similar methods be employed to evaluate social structure in other"solitary species"to better under-stand their social dynamics.

不同花粉来源对一年生植物种子性状和扩散能力的影响

与扩散有关的性状进化和表达与其他生活史功能交织在一起,并在各种生理约束条件下表现出来。这种关系可以在近交水平和扩散性之间得到预测,而且在解剖学和个体发育上联系在一起,从而使某个选择压力可能影响另外的一个。虽然近交对生殖成功和扩散策略的影响都引起了广泛关注,但只有少数研究同时考虑了这两者。此外,此类研究通常依赖于繁殖和扩散的表示:使用自交与异源杂交表示繁殖水平,使用扩散比表示扩散策略。本研究利用菊科Qep/ssancta的授粉实验,以两种不同的方式扩展繁殖和扩散的二分表示法。首先,我们使用授粉处理来表示一种统一连续体,即从亲缘授粉的自交到距离较远的邻居授粉。其次,我们不仅测量了繁殖成功率和扩散比,还测量了一整套连续的与形态和扩散相关的性状。研究结果显示,头状花序的比例,以及扩散的和非扩散的瘦果在自花传粉处理中都显著低于异源杂交处理。尽管自花授粉的植物很少产生不扩散的种子,但花粉来源对扩散比的影响统计上不显著。瘦果的生物量随亲本植物之间的距离增加而增加,但冠毛宽度没有增加,从而导致授粉对下落速度的影响不显着。总之,花粉来源主要影响与生殖产量有关的性状,但对主要与扩散有关的性状没有显著影响。繁殖和扩散性状对花粉来源变化响应的这种差异表明,与扩散有关的选择可能很弱和/或被其他因素所掩盖。