THE GENETICS OF ADAPTATION: THE GENETIC BASIS OF RESISTANCE TO WASP PARASITISM IN DROSOPHILA MELANOGASTER

There have been very few genetic analyses of “natural” adaptations, that is, those not involving artificial selection or responses to human disturbance. Here we analyze the genetic basis of geographic variation in Drosophila melanogaster's resistance to parasitism by a wasp, Asobara tabida. Our results suggest that population differences in ability to encapsulate parasitoid eggs have a fairly simple genetic basis: 60% of the D. melanogaster genome plays no role in differences between resistant and susceptible populations. Instead, resistance gene(s) are restricted to chromosome two, and may be further restricted to the centromeric region of this chromosome. This finding suggests that natural adaptations—like many responses to artificial selection and human disturbance—sometimes have a simple genetic basis.     

Gastrointestinal parasites of the Samango monkey,Cercopithecus mitis,in Natal,South Africa

Eight gastro-intestinal tracts of Cercopithecus mitis labiatus from Karkloof, Natal, and 121 fecal samples from C. m. erythrarchus from Cape Vidal, Natal, were examined for helminth parasites and/or their eggs. Fecal samples from six of the C. m. labiatus were examined for protozoan cysts. Five protozoon and six helminth species were identified from C.m labiatus. Most adult worms occurred in the caecum and colon, gut regions which also contained the highest volatile fatty acid levels. The eggs of nine helminth species were recovered from C. m. erythrarchus fecal samples; protozoans were not looked for in these samples.     

The opercular brood chambers of Spirorbidae

Brood chambers of Januinae are cuticular and have to be shed to liberate the larvae, whereas those of Pileolaria are bounded by two epithelia and are used repeatedly. Links for interpreting these differences are to be found amongst some of the smaller genera of Pileolariinae. In Amplicaria and Vinearia the embryos are held between a pair of opercular plates, which form distal and proximal cups with the concavities facing each other. They are successive units in a series of sheddings and renewals, found generally in Spirorbidae even on non-brooding opercula. A Janua brood chamber corresponds with the distal component of such a pair, the proximal component being represented by the basal plate. In most Pileolariinae the brood chamber is formed entirely by the proximal component. Amongst Nidificaria species, some hold the embryos in a simple cup with no distal protection, but others have the aboral side of the cup extended and growing over distally, like the dorsal lip of a blastopore. The aperture that remains may be almost closed but can open again to liberate the larvae. Brood chambers of Pileolaria are exactly like that, except that they lack any calcification proximally. Those of Jugaria and Bushiella are similar, but with additional protection through retention of distal plates. Protoleodora species are subarctic and very close to Jugaria and Bushiella in distribution and morphology, but they have less calcification, readily lose their distal plates, and develop soft-walled brood pouch extensions which can accommodate very large broods. There seem to be tenuous links between the Pileolariinae and the Romanchellinae, southern hemisphere spirorbids which incubate in their tubes. Fertilization and spawning need further study.     

Biology of a new species of socially parasitic thrips (Thysanoptera: Phlaeothripidae) inside Dunatothrips nests,with evolutionary implications for inquilinism in thrips

Akainothrips francisi sp. nov. is shown to be an inquiline (i.e. it invades, and breeds within, domiciles of another species). Currently, its only known host is Dunatothrips aneurae, a subsocial thrips that creates silken domiciles by securing together phyllodes of mulga (Acacia aneura) in the arid zone of Australia. We found Ak. francisi prolifically breeding inside live D. aneurae host domiciles, both immature and mature. Akainothrips francisi did not kill its host and we saw no evidence of antagonistic host‐inquiline interactions. This is thus the second demonstrably inquiline species of Acacia thrips, although other possible inquilines have been suggested including two Akainothrips. We found that Ak. francisi occurred with positive density dependence, and was associated with moderately reduced host reproduction. This latter association was especially evident in larger host domiciles, suggesting that Ak. francisi either inhibits further host reproduction after invasion or exploits poor quality hosts more successfully. Sex ratios were slightly female biased. Akainothrips francisi males were exceptionally variable in size, colour, and foreleg size compared to females, with morphs co‐occurring within domiciles, suggesting sexual selection and the possibility of different male reproductive strategies. The discovery of Ak. francisi highlights particular morphological affinities among known or suspected inquiline Acacia thrips within Akainothrips and other genera, allowing us to hypothesize a common origin of this lifestyle from within Akainothrips. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

A generalist brood parasite modifies use of a host in response to reproductive success

Avian obligate brood parasites, which rely solely on hosts to raise their young, should choose the highest quality hosts to maximize reproductive output. Brown-headed cowbirds (Molothrus ater) are extreme host generalists, yet female cowbirds could use information based on past reproductive outcomes to make egg-laying decisions thus minimizing fitness costs associated with parasitizing low-quality hosts. We use a long-term (21 years) nest-box study of a single host, the prothonotary warbler (Protonotaria citrea), to show that local cowbird reproductive success, but not host reproductive success, was positively correlated with the probability of parasitism the following year. Experimental manipulations of cowbird success corroborated that female cowbirds make future decisions about which hosts to use based on information pertaining to past cowbird success, both within and between years. The within-year pattern, in particular, points to local cowbird females selecting hosts based on past reproductive outcomes. This, coupled with high site fidelity of female cowbirds between years, points to information use, rather than cowbird natal returns alone, increasing parasitism rates on highly productive sites between years.     

Spatio‐temporal variation in European starling reproductive success at multiple small spatial scales

Understanding population dynamics requires spatio‐temporal variation in demography to be measured across appropriate spatial and temporal scales. However, the most appropriate spatial scale(s) may not be obvious, few datasets cover sufficient time periods, and key demographic rates are often incompletely measured. Consequently, it is often assumed that demography will be spatially homogeneous within populations that lack obvious subdivision. Here, we quantify small‐scale spatial and temporal variation in a key demographic rate, reproductive success (RS), within an apparently contiguous population of European starlings. We used hierarchical cluster analysis to define spatial clusters of nest sites at multiple small spatial scales and long‐term data to test the hypothesis that small‐scale spatio‐temporal variation in RS occurred. RS was measured as the number of chicks alive ca. 12 days posthatch either per first brood or per nest site per breeding season (thereby incorporating multiple breeding attempts). First brood RS varied substantially among spatial clusters and years. Furthermore, the pattern of spatial variation was stable across years; some nest clusters consistently produced more chicks than others. Total seasonal RS also varied substantially among spatial clusters and years. However, the magnitude of variation was much larger and the pattern of spatial variation was no longer temporally consistent. Furthermore, the estimated magnitude of spatial variation in RS was greater at smaller spatial scales. We thereby demonstrate substantial spatial, temporal, and spatio‐temporal variation in RS occurring at very small spatial scales. We show that the estimated magnitude of this variation depended on spatial scale and that spatio‐temporal variation would not have been detected if season‐long RS had not been measured. Such small‐scale spatio‐temporal variation should be incorporated into empirical and theoretical treatments of population dynamics.     

Bad guys turned nice? A critical assessment of Wolbachia mutualisms in arthropod hosts

Wolbachia are the most abundant bacterial endosymbionts among arthropods. Although maternally inherited, they do not conform to the widespread view that vertical transmission inevitably selects for beneficial symbionts. Instead, Wolbachia are notorious for their reproductive parasitism which, although lowering host fitness, ensures their spread. However, even for reproductive parasites it can pay to enhance host fitness. Indeed, there is a recent upsurge of reports on Wolbachia‐associated fitness benefits. Therefore, the question arises how such instances of mutualism are related to the phenotypes of reproductive parasitism. Here, we review the evidence of Wolbachia mutualisms in arthropods, including both facultative and obligate relationships, and critically assess their biological relevance. Although many studies report anti‐pathogenic effects of Wolbachia, few actually prove these effects to be relevant to field conditions. We further show that Wolbachia frequently have beneficial and detrimental effects at the same time, and that reproductive manipulations and obligate mutualisms may share common mechanisms. These findings undermine the idea of a clear‐cut distinction between Wolbachia mutualism and parasitism. In general, both facultative and obligate mutualisms can have a strong, and sometimes unforeseen, impact on the ecology and evolution of Wolbachia and their arthropod hosts. Acknowledging this mutualistic potential might be the key to a better understanding of some unresolved issues in the study of Wolbachia–host interactions.     

Telomere dynamics in parasitic great spotted cuckoos and their magpie hosts

Although little is known on the impact of environment on telomere length dynamics, it has been suggested to be affected by stress, lifestyle and/or life‐history strategies of animals. We here compared telomere dynamics in erythrocytes of hatchlings and fledglings of the brood parasite great spotted cuckoos (Clamator glandarius) and of magpies (Pica pica), their main host in Europe. In magpie chicks, telomere length decreased from hatching to fledging, whereas no significant change in telomere length of great spotted cuckoo chicks was found. Moreover, we found interspecific differences in the association between laying date and telomere shortening. Interspecific differences in telomere shortening were interpreted as a consequence of differences in lifestyle and life‐history characteristics of magpies and great spotted cuckoos. In comparison with magpies, cuckoos experience reduced sibling competition and higher access to resources and, consequently, lower stressful environmental conditions during the nestling phase. These characteristics also explain the associations between telomere attrition and environmental conditions (i.e. laying date) for magpies and the absence of association for great spotted cuckoos. These results therefore fit expectations on telomere dynamics derived from interspecific differences in lifestyle and life history of brood parasites and their bird hosts.