Major histocompatibility complex genes partly explain early survival in house sparrows.

Environmental factors and genetic incompatibilities between parents have been suggested as important determinants for embryonic mortality and survival. The genetic set-up of the immune system, specifically the highly polymorphic major histocompatibility complex (MHC) may also influence individual resistance to infections. MHC proteins are important for an appropriate adaptive immune response and enable T-cells to separate 'self' from 'non-self'. Here we investigate the importance of MHC functional diversity for early development in birds, more specifically, if offspring survival and body mass or size depends on number of different functional MHC alleles, specific functional MHC alleles or similarity of MHC alleles in the parents. Unhatched eggs are common in clutches of many bird species. In house sparrows (Passer domesticus), embryo and nestling mortality can exceed 50%. To control for environmental factors, our study was carried out on an aviary population. We found that one specific functional MHC allele was associated with reduced nestling survival, which was additionally supported by lower body mass and a smaller tarsus when nestlings have been 6 days old. Another allele was positively associated with tarsus length at a later nestling stage (nestlings 12 days old). These results indicate that MHC alleles might influence pathogen resistance or susceptibility.

Experimental evidence for costs due to chewing lice in the European bee-eater (Merops apiaster).

Animals frequently host organisms on their surface which can be beneficial, have no effect or a negative effect on their host. Ectoparasites, by definition, are those which incur costs to their host, but these costs may vary. Examples of avian ectoparasites are chewing lice which feed exclusively on dead feather or skin material; therefore, costs to their bird hosts are generally considered small. Theoretically, many possible proximate effects exist, like loss of tissue or food, infected bites, transmission of microparasitic diseases or reduced body insulation due to loss of feathers, which may ultimately also have fitness consequences. Here, we experimentally examined a possible negative impact of 2 feather-eating louse species (Meropoecus meropis and Brueelia apiastri) on male and female European bee-eaters (Merops apiaster) by removing or increasing louse loads and comparing their impact to a control group (lice removed and immediately returned) after 1 month. A negative effect of chewing lice was found on body mass and sedimentation rate and to a lesser extent on haematocrit levels. Males and females lost more weight when bearing heavy louse loads, and were more susceptible to infestations as indicated by the higher sedimentation rate. Our results further suggest differences in sex-specific susceptibility.

Traditional versus non-traditional nest-site choice: alternative decision strategies for nest-site selection.

In order to understand habitat selection, it is important to consider the way individual animals assess the suitability of a future reproductive site. One way of investigating mechanisms (such as those involved in nest site selection) is to examine breeding success and habitat characteristics in terms of animals returning to a place where they have already reproduced and using the same location over successive years or searching for new alternatives. This approach seems especially suitable for testing recent hypotheses suggesting that nest site selection is an integrative process that includes the use of social information (e.g. past breeding success of conspecifics). Determining the factors that elicit conservative or innovative behaviour regarding nest-site selection could be important for improving our understanding of habitat selection decisions in animals. More than half of the nests of the long-distance migratory lesser grey shrike Lanius minor, are built in the same or neighbouring trees. We found no evidence that habitat characteristics influence nest-site tradition. On the contrary, social information in terms of the presence of conspecifics and past reproductive success in terms of complete nest failures due to nest predation (but not detailed information such as variation in fledgling number) influenced nest-site tradition. Hence, social information and past reproductive success may play a role in nest-site choice in this species. Our results further demonstrate that previous experience with a nest site does not appear to be beneficial.

Costs and benefits of defences induced by predators differing in dangerousness.

While theoretical studies predict that inducible defences should be fine-tuned according to the qualities of the predator, very few studies have investigated how dangerousness of predators, i.e. the rate at which predators kill prey individuals, affects the strength of phenotypic responses and resulting benefits and costs of induced defences. We performed a comprehensive study on fitness consequences of predator-induced responses by involving four predators (leech, water scorpion, dragonfly larva and newt), evaluating costs and benefits of responses, testing differences in dangerousness between predators and measuring responses in several life history traits of prey. We raised Rana dalmatina tadpoles in the presence of free-ranging predators, in the presence of caged predators, and exposed naive and experienced tadpoles to free-ranging predators. Tadpoles adjusted the intensities of their behavioural and morphological defences to predator dangerousness. Survival was lower in the nonlethal presence of the most dangerous predator, while we could not detect costs of induced defences at or after metamorphosis. When exposed to free-ranging predators, small, but not large, tadpoles benefited from exhibiting an induced phenotype in terms of elevated survival when compared to naive tadpoles, but we did not observe higher survival either in tadpoles exhibiting more extreme phenotypes or in tadpoles exposed to the type of predator they were raised with. These results indicate that while predator-induced defences can mirror dangerousness of predators, costs and benefits do not necessarily scale to the magnitude of plastic responses.

Determinants of population biology of the chewing louse Brueelia apiastri (Mallophaga, Philopteridae) on the European bee-eater (Merops apiaster).

In this study we examine the population biology of Brueelia apiastri, a chewing louse living on the European bee-eater (Merops apiaster). We investigate the relationships between parasite intensity of infestation, sex ratio, reproductive output, parasite size and their environment i.e. the morphology, condition, age and sex of the host. Chewing lice were collected, their sex and age (developmental stage) identified and parasite body size determined as a measure of parasite condition (larger individuals consume larger meals and larger females may produce larger clutches). The data show that there is variation in intensity as well as body size of B. apiastri between individual bee-eaters and this variation is independent of the sex of the birds. However, size, condition and age of the birds seem to influence the infestation rates with B. apiastri. The study suggested size-dependent depredation, since more, smaller chewing lice (usually nymphs) living on birds in better condition and birds having longer bills. Furthermore, more male chewing lice (males are smaller than females) live on older birds. Intraspecific competition between parasites seems to have a negative effect on female but not male body size but this result could be also explained by size-dependent depredation.

Size versus health as a cue for host choice: a test of the tasty chick hypothesis.

Knowledge about how parasites choose their hosts is scarce and incomplete. Recent work has primarily focused on host health (i.e. immunocompetence) whereas ecological factors have been largely neglected. Here we investigate whether the immunocompetence, the nutritional condition or body size of nestling European bee-eaters Merops apiaster are used as parameters for habitat choice of the haematophagous fly Carnus hemapterus. We found that (i) flies consistently and nonrandomly preferred larger nestlings, even after controlling for differences in habitat availability (host surface), (ii) in the presence of similar-sized hosts, parasites' choice for an individual was less likely than if hosts differed in size, (iii) the more the hosts differed in size, the more the parasites aggregated on the larger nestling and (iv) parasites changed their preference according to size criteria regardless of the identity of the larger host. Neither immunocompetence nor host body condition could account for parasites' preference. Our results do not support the prediction of the Tasty Chick Hypothesis, namely that the poor immunocompetence ability of junior chicks makes them more attractive to parasites. We conclude that basic ecological factors (e.g. body size) can be essential for parasites when choosing a host.

Horizontal and vertical ectoparasite transmission of three species of Malophaga, and individual variation in european bee-eaters (Merops apiaster).

Dispersal of avian ectoparasites can occur through either vertical transmission from adult birds to their offspring in the nest or through horizontal transmission between adult birds or through phoresy. In this study, we investigated the importance of the 2 main transmission modes in the colonial European bee-eater and examined whether individual differences in ectoparasite intensity exist in relation to age, sex, and morphological features of the birds. The intensity of 3 chewing lice species was investigated. Almost all adult bee-eaters (98.3%, n = 176) were infested with 1 of the 3 ectoparasite species, whereas only 10.8% (n = 167) of all chicks were infested. Meropoecus meropis was the most frequent ectoparasite species on adult bee-eaters (prevalence 94.3%), whereas Meromenopon meropis was the most common species on chicks (prevalence 9.6%). Our results suggest that chewing lice are mainly horizontally transmitted among adult bee-eaters and mainly among pair members, whereas vertical transmission between parents and nestlings is less frequent. These conclusions were supported by a relation in ectoparasite intensity of pair members and a parasite removal experiment. Ectoparasite intensity was in general low in nestlings and did not correlate with ectoparasite intensity of their parents. Host age, sex, weight, and other morphological features did not explain variation in chewing lice infestation.

Faecal oestrogens and progesterone metabolites in mares of different breeds during the last trimester of pregnancy.

Non-invasive pregnancy diagnosis in mares by measuring faecal oestrogens has been performed over years with great accuracy. However, results have indicated breed-related differences in the amount of excreted steroids during late pregnancy. Therefore faecal samples were collected during the last 4 months of pregnancy of Thoroughbred (n = 10), New Forest pony (n = 9), Shetland pony (n = 10) and Iceland pony mares (n = 11). Concentrations of oestrogens, 20alpha-hydroxy- and 20-oxopregnanes were measured using enzyme immunoassays. Breed differences concerning both levels (though significant only in case of oestrogens) and time course of measured steroids were observed. There was a highly significant time effect (p < 0.00001) and an interaction between time and breeds (p < 0.02) for all steroids measured, suggesting that the time effect differs for different breeds. Oestrogen concentrations showed a decrease towards parturition, whereas in 20alpha-hydroxy- and 20-oxopregnane levels a pronounced increase was found 2 and I months, respectively, before parturition. A breed effect was only significant (p = 0.001) when comparing oestrogen concentrations and was mainly due to Iceland ponies, which had the lowest concentrations especially during the last 2 months of pregnancy. An almost significant (p = 0.06) breed effect was found for 20-oxopregnanes. In Iceland mares an additional increase in faecal pregnane content was already observed earlier, reaching maximum levels before the 60th day ante-partum (a.p.), followed by a decrease until the 30th day a.p. The ratio of 20-oxopregnanes to oestrogens in the samples was significantly higher (p < 0.006) in Iceland ponies in comparison with any other breed throughout all months before parturition. The breed differences observed in the amounts of oestrogens and/or progestagens present during late pregnancy may demonstrate micro-evolutionary changes in the endocrine system of a species.

Copulation rate and sperm use by female bearded tits, Panurus biarmicus.

We examined functional and mechanistic aspects of sperm competition in the bearded tit by determining (1) the variation in copulation rate between birds breeding alone or with other males present, and (2) the number of sperm present in the female reproductive tract estimated from the number of sperm trapped on the perivitelline layers of eggs. Females copulated at a higher rate with their partner when other males were present, but this did not translate into more sperm on eggs, possibly because insemination rates exceeded the female's sperm storage capacity. The rate of sperm loss from the female's reproductive tract, which is an important variable of sperm competition models, was obtained for the first time for a wild bird and was relatively high compared with other birds. This suggests that bearded tits copulate frequently because a single insemination is insufficient to fertilize the whole clutch, and females thus have to copulate during the egg-laying period to avoid infertile eggs. This finding is the first empirical support for the fertility insurance hypothesis. In line with this we discuss the significance of the interspecific variation in rate of sperm loss in relation to mating strategies in general, and the evolution of multiple mating rather than improved sperm storage in bearded tits with particular regard to the pronounced extrapair copulation behaviour of females. Copyright 1998 The Association for the Study of Animal Behaviour.