Effects of protein-constrained brood food on honey bee (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.) pollen foraging and colony growth

Pollen is the sole source of protein for honey bees, most importantly used to rear young. Honey bees are adept at regulating pollen stores in the colonies based on the needs of the colony. Mechanisms for regulation of pollen foraging in honey bee are complex and remain controversial. In this study, we used a novel approach to test the two competing hypothesis of pollen foraging regulation. We manipulated nurse bee biosynthesis of brood food using a protease inhibitor that interferes with midgut protein digestion, significantly decreasing the amount of protein extractable from hypopharyngeal glands. Experimental colonies were given equal amounts of protease inhibitor-treated and untreated pollen. Colonies receiving protease inhibitor treatment had significantly lower hypopharyngeal gland protein content than controls. There was no significant difference in the ratio of pollen to nonpollen foragers between the treatments. Pollen load weights were also not significantly different between treatments. Our results supported the pollen foraging effort predictions generated from the direct independent effects of pollen on the regulation of pollen foraging and did not support the prediction that nurse bees regulate pollen foraging through amount of hypopharyngeal gland protein biosynthesis.     

Intraspecific brood parasitism in the moorhen: parentage and parasite-host relationships determined by DNA fingerprinting

Parasitic female moorhens (Gallinula chloropus) lay from one to six eggs in the nests of conspecific neighbours. DNA fingerprinting was used to show that parasitic eggs could be correctly identified when they appeared in addition to or outside the host’s laying sequence. Moorhen hosts accept all parasitic eggs laid after the 2nd day of their laying period. To understand why moorhen hosts tolerate parasitic eggs, we tested two hypotheses. (1) The quasi-parasitism hypothesis: females lay their eggs in the evening when the host males are normally in attendance at the nest, so host males may allow parasitic females to lay in their nests in exchange for fertilizing their eggs. However, DNA fingerprinting showed that all the parasitic eggs were sired by the parasites’ mates. Parasitic moorhens frequently continue laying a clutch in their own nest, without a break in the laying sequence after a parasitic laying bout. The eggs laid by brood parasites in their own nests were also sired by their own mates. Therefore this hypothesis was rejected. (2) The kin selection hypothesis: if one or both members of the host pair are close relatives of the parasite, the costs of rearing parasitic chicks will be to some degree offset by inclusive fitness benefits. We examined the genetic relationships between parasites and their hosts using DNA fingerprinting and genealogical data. Natal philopatry by both sexes was relatively common in this population, and the probability that a neighbour of either sex was a first-order relative (parent-offspring) was calculated as 0.18. Although first-order relatives were not preferentially chosen as hosts over individuals that were not first-order relatives, even through random host selection there is almost a one-in-five chance that brood parasites in this population are closely related to their hosts. This may facilitate host tolerance of parasitic eggs. Other hypotheses are also discussed. Received: 3 February 1995/Accepted after revision: 27 August 1995     

Vitamin E supplementation enhances growth and condition of nestling barn swallows (Hirundo rustica)

To optimize fitness, organisms may have to trade the number and quality of individual offspring against their own condition and survival. Limiting micronutrients such as antioxidants may be crucial to this trade-off. We investigated whether vitamin E, a major antioxidant in the diet of vertebrates, is limiting to barn swallow (Hirundo rustica) nestlings. We manipulated brood size to alter the intensity of sib–sib competition and supplemented nestlings with two different physiological doses of vitamin E while establishing a control group. Treatment effects were measured on body mass and size, feather growth, T cell-mediated immune response and hematocrit. Supplementation with vitamin E at intermediate physiological doses improved nestling mass and condition and feather growth, whereas higher physiological doses did not enhance offspring quality compared to a control treatment. The positive effects of vitamin E on body mass and condition were only detectable from days 6 to 10 when maximum growth rate is attained. Experimental enlargement of broods reduced body mass and size and T cell-mediated immune response only during the late nestling period. The effect of vitamin E supplementation did not depend on brood size manipulation, as revealed by the nonsignificant statistical interaction. This result contradicts the hypothesis that availability of vitamin E depends on intrabrood competition and instead suggests that it depends on concentration of vitamin E in the insect prey of swallows. Thus, antioxidants may be available in limited amounts to barn swallow nestlings and such limitation affects growth. In addition, present results confirm that barn swallow parents trade progeny number against growth and immunity of individual offspring.     

Egg adoption can explain joint egg-laying in common eiders

Hypotheses regarding the evolution and maintenance of intraspecific nest parasitism were tested with data collected during a 3-year study of common eiders (Somateria mollissima) breeding near Churchill, Manitoba. The nest parasitism rate was highest (42.4% of nests) during the year with the highest nest density and the best environmental conditions, and lowest (20.2% of nests) in the year with the lowest nest density and the poorest environmental conditions. Over the nesting season, parasitic eggs were laid at the same time as normally laid eggs. Most parasitic eggs (>75%) were laid before the host female laid her third egg. The majority of the parasitic eggs were the first or second egg produced by the parasitic female. When a parasitic egg was laid before or on the same day as the host female initiated her clutch, the probability of her first egg being depredated before incubation was significantly lowered. First- and second-laid eggs suffered a high rate of predation probably because nesting females do not attend their clutch until their second or third egg is laid. Hypotheses that some females use intraspecific nest parasitism to parasitize the parental care of other females were inconsistent with these data. Egg adoption is a likely explanation for the prevalence of females incubating parasitic eggs in this population. Received: 30 September 1997 / Accepted after revision: 6 May 1998     

Defending young biparentally: female risk-taking with and without a male in the burying beetle, <Emphasis Type="Italic">Nicrophorus pustulatus</Emphasis>

A positive correlation between the parental effort of a male and female should promote stable biparental care. Risk-taking (as assessed by injuries) against infanticidal intruders by Nicrophorus pustulatus females was expected to be low when females had a low probability of successful defense of the young. I tested the hypothesis that when the presence of a male partner increased the probability of successful defense from low to moderate that female risk-taking would increase. Single females and pairs with first instar larvae were confronted by potentially infanticidal male and female conspecific intruders. Male intruders routinely took over nests from unpaired females (30 of 36 trials). Unpaired females and male intruders were injured infrequently, indicating less intense fights despite the high probability of infanticide. A resident female defending against a male intruder was injured more often when paired than unpaired, suggesting greater risk-taking. A male parent that delays desertion, therefore, receives fitness benefits not only from his own defense of the young, but from greater female defense against male intruders as well. It is hypothesized that the threat of infanticidal takeovers by males promotes extended biparental care in burying beetles. When the intruder was female, on the other hand, a female parent on her own had a moderate probability of successfully defending the brood (22 of 36 trials). The presence of a male partner against female intruders almost guaranteed successful defense (35 of 36 trials) and female intruders did not appear to contest pairs vigorously. Against female intruders the presence of a male partner did not significantly change injury rates of the defending female.     

First evidence of regular common cuckoo, <Emphasis Type="Italic">Cuculus canorus</Emphasis>, parasitism on eastern olivaceous warblers, <Emphasis Type="Italic">Hippolais pallida elaeica</Emphasis>

Coevolution is defined as specialized relationships between species that lead to a reciprocal evolutionary change. A particularly suitable model system for studying coevolution is the interactions between obligate avian brood parasites and their hosts. The common cuckoo (Cuculus canorus, hereafter cuckoo) is a well-known brood parasite, which utilizes a range of smaller passerines as hosts. However, warblers of the genus Hippolais have rarely been reported as being victims of cuckoos, and furthermore, few data exist on the occurrence of antiparasite defenses in these hosts. In this study, we examined possible host–parasite coevolution between cuckoos and eastern olivaceous warblers (Hippolais pallida elaeica, hereafter olivaceous warblers) in three closely situated areas in northwestern Bulgaria. The olivaceous warbler has never been reported to be a regular cuckoo host. However, the present study, carried out in 2001–2003 shows that the olivaceous warbler is regularly and heavily parasitized by the cuckoo in this area. Parasitism rate was high (26.6%, 34/128) and consistent among years, with some variation between areas. The cuckoo egg mimicry was moderately good, and olivaceous warbler rejection rate of such eggs was 50%. Cuckoo eggs laid in olivaceous warbler nests had a whitish to whitish-green ground color, and the majority appeared to be distinctly different from cuckoo eggs found in other host species in the area. The olivaceous warbler proved to be a rather good host for cuckoos as 20.6% (7/34) of cuckoo eggs laid produced fledglings, a breeding success comparable to other suitable hosts in Europe. This is the first in-depth study of brood parasitism in a warbler of the genus Hippolais, and cuckoos parasitizing olivaceous warblers probably represent a previously unknown gens.