Ecological effects of sex differ with trophic positions in a simple food web

Sexual differences in parental investment, predation pressure, and foraging efforts are common in nature and affect the trophic flow in food webs. Specifically, the sexual differences in predator and prey behavior change in trophic inflow and outflow, respectively, while those in parental investment alter the reproductive allocation of acquired resources in the population. Consequently, these factors may play an important role in determining the system structure and persistence. However, few studies have examined how sexual differences in trophic flow affect food web dynamics. In this study, I show the ecological role of sex by explicitly incorporating sexual differences in trophic flow into a three‐species food web model. The results demonstrated that the ecological waste of males, that is, the amount of trophic inflow into males with less parental investment, plays an important role in system persistence and structure. In particular, the synergy between sexual differences in parental investment and trophic inflows and outflows is important in determining web persistence: Significant impacts of male‐biased trophic flows require the condition of anisogamy. In addition, the dynamic effects of the ecological waste of males differ with trophic level: The coexistence of a food web occurs more frequently with biased inflows into predator males, but occurs less frequently with biased inflows into consumer males. The model analysis indicates that investigating the pattern of sexual differences among trophic positions can enrich our understanding of food web persistence and structure in the real world.     

Versatility and specialization in labrid fishes: ecomorphological implications

Summary The term specialized has been used to describe species that possess unique functional attributes and/or a narrow, stereotyped range of attributes, but there are few comparative functional analyses of specialists and generalists. If species with functional morphological specializations are capable of functioning over a broad range, the link between morphology and ecology may be relaxed under certain environmental conditions. In this study, high-speed films of jaw movements during prey capture were compared statistically for three coexisting coral reef fish species in the family Labridae, one trophic specialist and two trophic generalists. The trophic specialist possessed a unique functional feature related to the movement of the hyoid in the floor of the mouth, while the trophic generalists were not observed to possess any functional specializations. All three species showed functional versatility in that they were able to adjust their prey capture mechanism in response to the evasive potential of the prey. The functional versatility of trophic specialists has implications for ecomorphological studies, since species characterized as possessing unique functional or morphological features may demonstrate marked flexibility in ecological variables such as diet or foraging behavior, decreasing the likelihood of identifying correlations between morphology and ecology.     

Sex Differences in Retrieval Behavior by the Biparental Convict Cichlid

Biparental species occasionally demonstrate a division of roles in which parents perform sex-typical tasks, with females offering direct care and spending the majority of their time with the offspring while males are more indirect in their care, providing the majority of defense against potential brood predators. To examine the flexibility in the sex-typical roles shown by convict cichlids ( Amatitlania nigrofasciata ), we displaced non-swimming young at three different distances from the nest and then analyzed the retrieval behaviors of each parent. Retrieval of altricial young is a behavior commonly used to measure parental care in mammalian studies, but has rarely been used in other taxa. We found sex differences in retrieval behavior: on average, females retrieved young close to the nest and males retrieved young far from the nest. This difference in parental contribution suggests a division of labor with sex-specific roles. Sex differences may be due to proximity to young and/or apparent risk of offspring predation. Additionally, we found that latency to first retrieval and total time spent retrieving young remained consistent across the various displacement distances, suggesting that retrieval is an essential parental behavior. Additionally, we include observations of wriggler retrieval by parents in a natural population of Costa Rican convict cichlids.     

The role of androgens in the trade-off between territorial and parental behavior in the Azorean rock-pool blenny, Parablennius parvicornis

Androgen hormones have been shown to facilitate competitive ability in courtship and territorial behavior, while suppressing paternal behavior. The rock-pool blenny, Parablennius parvicornis, provides an excellent model to study the proximate regulation of such a trade-off between territorial and parental behavior, because nest-holder males of this species display these behaviors simultaneously. A field study was carried out in which territorial nest holder males were either treated with long-lasting implants filled with 11-ketotestosterone (11-KT) or with control implants. Males treated with 11-KT showed a higher frequency of aggressive behavior, were more responsive to aggressive challenges, and were more persistent in aggressive behavior than control males. In addition, territories were larger in males treated with 11-KT than in controls. We found evidence for incompatibility between defense of a large territory and high levels of parental behavior. However, contrary to expectation, 11-KT did not suppress parental behavior. We suggest that trade-offs between territorial and parental behavior may not be regulated by androgen hormones but may result from a time constraint in the individual's activity budget.     

The Roles of Stimuli from Young, Previous Breeding Experience, and Prolactin in Regulating Parental Behavior in Ring Doves (Streptopelia risoria)

In addition to stimulating crop "milk" formation in ring doves, prolactin (PRL) may promote the parental regurgitation behavior that transfers this "milk" to the young at the time of hatching. Although earlier studies suggest that previous breeding experience is an important modulator of PRL-induced parental regurgitation behavior in ring doves, the ways in which experience, hormones, and stimuli from young interact to promote parental behavior have not been well characterized in this species. In the first study, untreated, nonbreeding female doves with and without previous breeding experience were given 10 daily parental behavior tests (2 h/day) with a hungry 5- to 10-day-old foster squab. Experienced females exhibited a higher incidence of regurgitation behavior, defensive behavior, and crouching or sitting in the nest than did inexperienced females. In a second study, nonbreeding females were given 10 daily tests for parental behavior while they received sc injections of ovine PRL or vehicle. Prolactin reduced squab-directed aggression and increased the incidence of regurgitation feeding behavior of foster squabs in both experienced and inexperienced females. However, the average number of regurgitation feeding acts displayed by those PRL-treated females that showed the behavior was over eight times higher in experienced females than in inexperienced females. Previous experience also enhanced the stimulatory effects of PRL on defensive behavior and crouching or sitting in the nest. The parental behavior exhibited by nonbreeding, PRL-treated experienced females was qualitatively and quantitatively similar to that observed in normally breeding females during a single test with their own hungry 5- to 10-day-old squabs. These findings indicate that PRL and previous breeding experience both enhance the parental responsiveness of nonbreeding female doves and that under optimal hormonal, experiential, and squab exposure conditions, nonbreeding doves exhibit levels of parental activity that rival those of normally breeding parents.     

Eulittoral macroinvertebrate communities of lowland lakes: discrimination among trophic states

1. Nutrient inputs from urban and agricultural land use often result in shifts in species composition of pelagic and profundal invertebrate communities. Here, we test if nutrient enrichment affects the composition of eulittoral macroinvertebrate communities, and, if so, if macroinvertebrate communities of five different habitat types reflect differences in trophic state. 2. Macroinvertebrate community composition of 36 lakes was significantly correlated with total phosphorus (TP) concentration, the proportion of coarse woody debris (CWD) and root habitats and the proportion of grassland. 3. However, macroinvertebrate communities of five major habitat types from eight lakes were more dissimilar among habitats than among trophic states. Community composition of reed and stone habitats was significantly correlated with wind exposure but not TP concentration, while macroinvertebrate composition of sand habitats was related to TP concentration and coarse sediments. In CWD and root habitats, both TP concentration and a predominance of invasive species covaried, which made it difficult to relate the observed compositional differences to either trophic state or to the effects of competition between native and invasive species. 4. Trophic state influenced the composition of eulittoral macroinvertebrate communities but to a lesser extent than has been previously reported for profundal habitats. Moreover, the effects of trophic state were nested within habitat type and were partially superseded by biotic interactions and small‐scaled habitat complexity. Although eulittoral macroinvertebrate communities were not strong indicators of the trophic state of lowland lakes, they may be used to assess other anthropogenic impacts on lakeshores.     

PATTERNS OF PARENTAL CARE AND PARENTAL INVESTMENT IN MARSUPIALS

I. Information on growth, development and care of young has been assembled for 62 species of marsupial. 2. During gestation, development of the marsupial embryo proceeds only so far as to allow the neonate to make its way from the urogenital opening to the mammary area on the abdomen of the female where it attaches to a teat. Specific structural adaptations keep the neonate firmly attached to the teat for at least the first month after birth. 3. Six types of pouch are distinguished ranging from lateral folds of skin, which do not cover the mammary area or enclose the developing young, to a fold of skin that covers the mammary area and forms a deep pouch, completely enclosing the developing young. 4. Although the young is very small at birth and birth is rapid, specific changes in the behaviour of females occur around the time of birth, and a specific birth position is adopted. 5. The time at which marsupial young leave the pouch cannot be equated with birth in eutherians, because of the considerable variations in the type of pouch and in patterns of parental care. From a consideration of the functional development of the young in the pouch, it is suggested that the nearest equivalent to eutherian birth is the time at which the marsupial young achieves homeostasis, when it is well furred and endothermic. 6. Maternal behaviour is influenced by the type of pouch. In all species, the mother keeps the young and the pouch clean by licking, especially when the young are wholly within the pouch or attached to the abdomen. In species with reduced pouches where young are left in a nest at an early stage of development, maternal behaviour includes nest building, defence, and retrieving and carrying the young. These functions are performed by the pouch itself in species with large deep pouches in which the young is carried for a much larger part of its development, and other specific maternal behaviours are infrequent. 7. The patterns of parental care are reviewed over all families of marsupial. Not all members of a family have the same pattern of parental care, which appears to be influenced by many factors including body size, type of pouch, diet, litter size and other aspects of life history strategy. 8. Three patterns of parental care are distinguished: (A) As soon as young begin to release the teat they are no longer carried by the mother, and are left in a nest when still barely furred, ectothermic and before the eyes open. This pattern is found in species with large litter size and a pouch reduced or absent, e.g. some Dasyuridae and some Didelphidae. (B) Young remain in the pouch after they begin to release the teat but are left in a nest, at a later stage of development than in A, when well furred, endothermic and with eyes open. After first pouch exit, there is generally a period when young return to the pouch from time to time. This pattern is found in species with well developed pouches and litters of I or > 1 e.g. Peramelidae, some Didelphidae. (C) Young remain in the pouch after they begin to release the teat. At first pouch exit, the young is well furred and endothermic, and leaves the pouch only for brief periods, gradually spending more time out until permanent pouch exit. It is not usually left in a nest. This pattern is found in species with well developed pouches and litters of one, e.g. Macropodidae. 9. Pattern A is seen particularly in the smaller species in any family, where large litter size means that by the time young release the teat, the litter is about 50% of maternal body weight and a considerable burden. In such species, young are left in a nest as soon as possible. In larger species with patterns B or C, litter size is smaller, and by the time they are no longer carried by the female, the litter is still only 20% of maternal weight. 10. Whatever the pattern of parental care, mortality from birth to permanent pouch exit is not unusually high in marsupials in comparison with eutherians. 11. I suggest that the presence of the pouch and the associated patterns of parental care are important determinants of social organization in marsupials. For much of the period of dependence, the young is small, attached to a teat or in a pouch. The male can make little contribution to parental care, and there is little room for improvement in the care of young in complex social groups. In most species, the female on her own is sufficient caretaker. The male is most likely to increase his own biological fitness by going off to mate again and leaving the female to raise his offspring. 12. Patterns of energy expenditure on offspring by female marsupials were assessed throughout the development of young. Investment before birth was assessed by weight of the neonate, during development by growth rate and the time for which the young was carried (pouch life), and total investment by weight of young at weaning and time from birth to weaning. Regression of measures of investment against maternal body weight allowed comparison of investment in animals of different size. 13. Investment in young before birth is very small. Neonatal marsupials range in size from 0·01 to 1 g, and the largest is less than 0·2 % of the size of the mother. Larger mothers produce larger young which are smaller relative to the mother than are the young of smaller species. Individual young in the family Dasyuridae are particularly small. 14. Growth rates in g/d were calculated over the period from permanent pouch exit to weaning. There is a very close correlation between growth rate and maternal body weight - that of litters increases as the 0·78 power of body weight. During this period the growth rate of individuals is comparable with that of eutherian young during lactation, and in litters it is higher still, suggesting that the difference in patterns of growth are not due to the lower metabolic rate of marsupials. As in eutherians there is considerable individual variation in growth rate; it is very high in litters of small dasyurids, which have individual rates comparable to those of larger species. Young of the family Peramelidae grow and develop rapidly; those of the arboreal folivore Phascolarctos do both slowly. I 5. Pouch life, the period for which the young is carried by the mother, increases with body size; as expected, species with pattern A parental care have shorter pouch lives than species of the same size with patterns B or C, reflecting the early stage of development at which young are left in the nest in pattern A. 16. Time from birth to weaning is also longer in larger species. There is a close relationship of age at weaning with maternal weight, with some significant exceptions. For their size, the family Peramelidae have a very short time from birth to weaning, and the time from pouch exit to weaning is particularly short. Many arboreal species have longer periods of dependence than expected from their size. 17. The weight at weaning of individual young is closely related to MBW^0·71, but the weight of one young relative to maternal body weight shows no trend with size, and ranges from 25–61 %, with a mean of 42 %. 18. Parental Investment, as measured by the function Wt. of litter at weaning × 100/MBW, decreases with increasing size of mother as MBW^0·28. The highest levels of investment are found in very small species. In many small species of the family Dasyuridae, a litter at weaning is > 300% MBW. By contrast, investment in the family Peramelidae is low - at weaning a litter of three is about 50% MBW, comparable with investment in a single young of the family Macropodidae. 19. The evolution of patterns of parental care and investment appears to follow three main lines: (1) Species with large litter size, high levels of investment in litters and in individual young. Investment is directed to growth and not to carrying the young in the pouch, since young are left in a nest at an early stage. Typical of this group is the family Dasyuridae, in which many species make few reproductive attempts per year. (2) Species with litters of more than one, low levels of investment in litters and in individuals, but rapid growth and development of young. Because of the small relative size of young they are carried in the pouch for a large part of the period from birth to weaning. This pattern is shown by the family Peramelidae, and seen as an adaptation to rapid and repeated reproduction in an environment with an extended favourable season. (3) Species with small litter size, lower total investment, but investment in individual young is not low, and investment in carrying young to an advanced stage of development is high. Patterns of this type are found in the Diprotodonta, with extreme development in the Macropodidae. 20. Many of the measures of investment have been expressed as a power function of maternal body weight. The exponents of body weight in these functions are such as to suggest that an important underlying variable is metabolic rate. 21. It has been suggested elsewhere that the marsupial mode of reproduction evolved as an adaptation to environmental uncertainty, in that it allows a reproductive attempt to be abandoned at any time much more readily than in eutherians, thereby increasing the likelihood that a female will survive to reproduce again. I consider this suggestion in the light of patterns of parental investment. For small, short-lived species, any reproductive attempt represents a substantial part of its lifetime reproductive output. Investment in any one reproductive attempt is high, and the cost of replacing an abandoned attempt is so high that it seems unlikely that the desertion of offspring would be an important reproductive strategy in small ancestral marsupials, although it may be an important response to environmental uncertainty in certain large modern macropodids.     

Speckled warblers break cooperative rules: absence of helping in a group-living member of the Pardalotidae

In the majority of cooperatively breeding bird species, subordinates help the dominant pair to provision the young, regardless of the origin of groups and relatedness between members. Within the family that includes speckled warblers, Chthonicola sagittata, there is considerable variation in social organization and parental behaviour, but the societies of other group-living species in this family are of kin, and subordinates provision the young of breeders. Speckled warblers differ in that offspring are never philopatric, and breeding groups comprise unrelated individuals. We used behavioural observations and DNA fingerprinting to examine genetic parentage and the mating system of the group-living speckled warbler in Canberra, Australia. Speckled warblers breed as pairs or in trios consisting of a female with two males. Alpha males are socially dominant to beta males and maintain dominance through aggression. Beta males never helped to feed nestlings or fledglings, even though they competed for copulations and in one case gained paternity of two of three young in a brood. The social system is therefore polyandrous but not cooperative. As well as competing for copulations with females on their own territories, beta males and single males (those that had lost their breeding partner) regularly undertook extraterritorial forays, most often when the neighbouring female was fertile. Failure by beta males to help even with broods containing their own offspring may be adaptive in this species and may result from increased opportunity for extrapair fertilizations or enhancement of prospects for future reproduction through the formation of alliances with females.     

Scale-eating in characoids and other fishes

Synopsis Scale-eating is known for several unrelated fish groups, but few data are available on the habits of most species. General habits and feeding behavior of some lepidophagous characoids are presented and compared to other scale-eating species. The diversity of morphology, habits, and behavior of scale-eating fishes is great, and few patterns are shared by the specialized scale-eaters. Except for modified teeth, no morphological characteristic permits identifying a fish as a specialized lepidophage. Hunting tactics consist mainly of ambush, stalking, or disguise (aggressive mimicry). Scale-removal may be accomplished by a jarring strike with the snout, generally directed at the prey's flank, or by biting or rasping. The mode of scale-removal seems to reflect primarily the disposition of the jaws and the teeth. Scales are swallowed directly if taken in the mouth; if not, they are gathered as they sink, or picked up from the bottom. Scale-eating is probably a size-limited habit. Specialized scale-eaters rarely exceed 200 mm, most ranging near 120 mm. Some species eat scales only when young; most take other food items in addition to scales. Scale-eating habits probably arose from trophic or social behaviors. These are not mutually exclusive and, indeed, may have acted together during the evolution of lepidophagy. Suggested trophic origins include scraping epilithic algae, modified piscivory, and necrophagy. Social origins include intra- and interspecific aggressive behavior during feeding.     

Mating system and kin relationship between adults and young in the shell-brooding cichlid fish <Emphasis Type="Italic">Neolamprologus meeli</Emphasis> in Lake Tanganyika

Mating system and parental behavior of ten monogamous pairs and two polygynous groups of the Tanganyikan cichlid Neolamprologus meeli were observed in their natural habitat. The home ranges of males and females overlapped with each other. Most groups included one to six young. Paternal and maternal relationships were determined for 22 young from DNA microsatellite markers. Three types of kinship were found: (I) kinship to both the male and female; (II) kinship to females only; and (III) non-kinship to both sexes. In the groups with type II young, step-fathering or sneaking may have occurred. Type III young were larger than type I, suggesting that the former were of sufficient size to leave their birth nest and settle in the territories of foster parents. Both males and females drove out potential predators of young (including three species of Lepidiolamprologus) as a parental behavior. Adults with type III young attacked approaching predators with as much frequency as those with type I young only, indicating that they provided alloparental care. Adults and young swam together, but, a significant difference existed in the frequencies of interactions between adults versus kin young and adults versus non-kin young. The results suggest that both adults and young recognized kin. Electronic Publication     

Evolution of reversed sex roles, sexual size dimorphism, and mating system in coucals (Centropodidae, Aves)

The evolution of greater male than female parental care remains poorly understood. In birds it is thought to be related to precocial chicks and small clutch size. This review shows, however, that such role reversal has also evolved in a family with altricial young and relatively large clutch size: coucals (Centropodidae, Cuculiformes). Males perform most nest building, incubation, and feeding of young. As predicted by sexual selection theory, coucals have also reversed sexual size dimorphism, females being larger than males in all 12 species for which size data are available. Most coucals that have been studied are monogamous, but the black coucal Centropus grillii appears to be polyandrous, and males perform almost all parental care, whereas females show more active advertisement behaviour. In this species, females are about 50% heavier than males. Polyandry in the black coucal seems to be associated with a shift to a habitat with seasonally rich food resources. Difficulties for female coucals of gathering enough resources for producing several clutches of relatively large eggs may favour mainly male parental care. Female sexual competition and resource storage, and male foraging economy, may explain why females are larger. Additional field studies are needed to test these hypotheses; the coucals are of great interest to sexual selection and mating systems theory.     

Predominant female care in the beetle Lethrus apterus with supposedly biparental care

Although intensive care for offspring by both parents is rare in arthropods, it occurs in some species including the beetle Lethrus apterus. According to previous publications, in this species the male collects leaves, which are used by the female to form balls in the underground nest burrow. These balls serve as food for the hatched offspring. Most knowledge about the behavior of this species is based on information collected more than a century ago. Therefore, we investigated above‐ground breeding behavior and the status of nest burrows of this beetle in its natural habitat in Hungary. Our results suggest that contrary to previously documented cases, above‐ground parental care, i.e. the collection of leaves, is done predominantly not by the males but the females. Further research is needed to understand the role of the sexes in parental care in this species and to explain the discrepancy between the previously documented cases and the results we report here.     

Trophic ecology of two savanna grazers,blue wildebeest <Emphasis Type="Italic">Connochaetes taurinus</Emphasis> and black wildebeest <Emphasis Type="Italic">Connochaetes gnou</Emphasis>

The feeding niches and trophic ecology of two South African grazers, blue wildebeest Connochaetes taurinus and black wildebeest Connochaetes gnou, are compared using stable carbon and nitrogen isotope data from feces and tooth dentine collagen. As sympatric, closely related taxa predicted to occupy similar trophic positions, the blue and black wildebeest provide a good model for studying the mechanisms of coexistence and macroevolution in mammals. Data from feces collected from a single reserve in the Free State Province reveal different trophic behaviors between two herds of blue wildebeest and between both compared with a single herd of black wildebeest. These data suggest that sympatric coexistence of blue and black wildebeest is facilitated by differential niche occupation at family group or herd levels, rather than between species. However, such separation does not occur over longer time scales: results from dentine collagen support the hypothesis that the two species are indistinct in terms of trophic behavior, although blue wildebeest show more feeding flexibility, probably because of their wider habitat tolerance range. Similarities in premaxillary width of males and females of both species also suggest that both species are adapted to similar feeding styles. Thus, it is unlikely that changes in trophic behavior provided the trigger for divergence of the black from the blue wildebeest lineage in the Middle Pleistocene. We argue that the case of these two species represents an example of speciation that was not driven by resource competition, as is often assumed for many turnover events in mammalian evolution. We briefly discuss a previous suggestion that links black wildebeest evolution to their more territorial breeding behavior associated with Middle-to-Late Pleistocene landscape changes in southern Africa.     

Exploring the Relation of Harsh Parental Discipline with Child Emotional and Behavioral Problems by Using Multiple Informants. The Generation R Study

Parental harsh disciplining, like corporal punishment, has consistently been associated with adverse mental health outcomes in children. It remains a challenge to accurately assess the consequences of harsh discipline, as researchers and clinicians generally rely on parent report of young children''s problem behaviors. If parents rate their parenting styles and their child''s behavior this may bias results. The use of child self-report on problem behaviors is not common but may provide extra information about the relation of harsh parental discipline and problem behavior. We examined the independent contribution of young children''s self-report above parental report of emotional and behavioral problems in a study of maternal and paternal harsh discipline in a birth cohort. Maternal and paternal harsh discipline predicted both parent reported behavioral and parent reported emotional problems, but only child reported behavioral problems. Associations were not explained by pre-existing behavioral problems at age 3. Importantly, the association with child reported outcomes was independent from parent reported problem behavior. These results suggest that young children''s self-reports of behavioral problems provide unique information on the effects of harsh parental discipline. Inclusion of child self-reports can therefore help estimate the effects of harsh parental discipline more accurately.     

Care of young and the effect of the presence of a male on parental behavior in the common vole (Microtus arvalis) in captivity

Care of the young by male and female common voles reared by both parents (complete families) or by females only (incomplete families) has been studied. It has emerged that the absence of an adult male in the common vole family groups, reducing the care of young (first and foremost, tactile stimulation), negatively influences their pair bonds and the subsequent parental behavior of the male offspring.     

Control of parental investment changes plastically over time with residual reproductive value

Evolutionary conflict between parents and offspring over parental resource investment is a significant selective force on the traits of both parents and offspring. Empirical studies have shown that for some species, the amount of parental investment is controlled by the parents, whereas in other species, it is controlled by the offspring. The main difference between these two strategies is the residual reproductive value of the parents or opportunities for future reproduction. Therefore, this could explain the patterns of control of parental investment at the species level. However, the residual reproductive value of the parents will change during their lifetime; therefore, parental influence on the amount of investment can be expected to change plastically. Here, we investigated control of parental investment when parents were young and had a high residual reproductive value, compared to when they were old and had a low residual reproductive value using a cross‐fostering experiment in the burying beetle Nicrophorus quadripunctatus. We found that parents exert greater control over parental investment when they are young, but parental control is weakened as the parents age. Our results demonstrate that control of parental investment is not fixed, but changes plastically during the parent's lifetime.     

The evolution of parental care in freshwater leeches

Summary The life-history strategies of a selection of the most common European freshwater leeches (Euhirudinea) are described. On the basis of this information and results from the literature, the probable phylogenetic development of parental care in the Euhirudinea is reconstructed. The jawless worm leeches (Erpobdellidae) secrete a protective cocoon, cement it to the substrate and sometimes ventilate it before they leave the egg capsules. This behaviour represents the most ancient state in leech evolution. Members of the jawed Hirudinidae deposit desiccation-resistant cocoons on land. All known Glossiphoniidae (leeches equipped with a proboscis) have evolved the habit of brooding the eggs and young. These unique parental care patterns within one family of extant freshwater leeches can be arranged schematically in a series of increasing complexity which may reflect the evolution of brooding behaviour. Glossiphoniid leeches of the genus Helobdella, which have a world-wide distribution, display the most highly developed parental care system: they not only protect but also feed the young they carry. This results in the young being much larger when they leave the parent and, presumably, in higher subsequent survival. Isolated cocoons of all aquatic leeches are rapidly destroyed by predators, primarily water snails. In erpobdellids (but not glossiphoniids, which protect the cocoons) a large portion of the cocoons are lost due to predatory attacks. We conclude that the major selective pressure driving the evolution of parental care in leeches may have been predation on eggs and juvenile stages. Dedicated to Professor Dr. G. Osche on the occasion of his 75th birthday     

Trophic dynamics within a hybrid zone – interactions between an abundant cyprinid hybrid and sympatric parental species

1. Recent proliferation of hybridisation in response to anthropogenic ecosystem change, coupled with increasing evidence of the importance of ancient hybridisation events in the formation of many species, has moved hybridisation to the forefront of evolutionary theory. 2. In spite of this, the mechanisms (e.g. differences in trophic ecology) by which hybrids co‐exist with parental taxa are poorly understood. A unique hybrid zone exists in Irish freshwater systems, whereby hybrid offspring off two non‐native cyprinid fishes often outnumber both parental species. 3. Using stable isotope and gut content analyses, we determined the trophic interactions between sympatric populations of roach (Rutilus rutilus), bream (Abramis brama) and their hybrid in lacustrine habitats. 4. The diet of all three groups displayed little variation across the study systems, and dietary overlap was observed between both parental species and hybrids. Hybrids displayed diet, niche breadth and trophic position that were intermediate between the two parental species while also exhibiting greater flexibility in diet across systems.     

Prolactin and helping in birds: has natural selection strengthened helping behavior?

The evolution of helping behavior in birds has been hotly debated.Hamilton's inclusive fitness theory has received much supportfrom ecological cost-benefit studies; however, the hypothesisthat helping has not been selected per se but is simply a phenotypicallyplastic response to altered social conditions has been proposed.In this view helping by nonbreeding birds occurs when at independencethey fail to leave their parents and are exposed to the criticalstimulus, the begging of young birds to be fed. We report thatlevels of prolactin, a hormone associated with parental behavior,are conspicuously higher in an avian species with helpers, theMexican jay (Aphelocoma ultramarina), than in a congeneric andsympatric species without helpers, the western scrub jay (A.californica). Specifically, prolactin in the nonbreeding membersof the helping species is higher than the level found in thebreeders of the congeneric nonhelping species. In addition,prolactin levels in nonbreeders rise well before the appearanceof begging young. These findings reject the phenotypic plasticityhypothesis based purely on a response to begging young and suggestthat prolactin is involved in the physiology of helping behaviorin birds as part of a complex adaptation.     

Anatomy of the mechanosensory lateral line canal system and electrosensory ampullae of Lorenzini in two species of sawshark (fam. Pristiophoridae)

It has long been assumed that the elongated rostra (the saws) of sawsharks (family: Pristiophoridae) and sawfish (family: Pristidae) serve a similar function. Recent behavioural and anatomical studies have shed light on the dual function of the pristid rostrum in mechanosensory and electrosensory prey detection and prey manipulation. Here, the authors examine the distributions of the mechanosensory lateral line canals and electrosensory ampullae of Lorenzini in the southern sawshark, Pristiophorus nudipinnis and the longnose sawshark, Pristiophorus cirratus. In both species, the receptive fields of the mechano- and electrosensory systems extend the full length of the rostrum indicating that the sawshark rostrum serves a sensory function. Interestingly, despite recent findings suggesting they feed at different trophic levels, minimal interspecific variation between the two species was recorded. Nonetheless, compared to pristids, the pristiophorid rostrum possesses a reduced mechanosensory sampling field but higher electrosensory resolution, which suggests that pristiophorids may not use their rostrums to disable large prey like pristids do.