Brood desertion in Kentish plover: the value of parental care

To understand the evolution of parental care, one needs to estimatethe payoffs from providing care for the offspring and from terminatingcare and deserting them. In this study we estimated the payofffrom care provision, and in a companion paper we analyze thepayoff from offspring desertion. In the current study we experimentallyinvestigated the influence of the number and sex of attendingparents on growth and survival of offspring in the Kentish ploverCharadrius alexandrinus, in two sites (A and B). Either the maleor the female parent was removed from some broods at hatchingof the chicks (female-only and male-only broods, respectively),whereas in control broods both parents were allowed to attendtheir young. At site A survival of the chicks was lower in uniparental(male-only and female-only) broods than in control broods, whereaswe found no difference in brood survival at site B. Brood survivaldecreased over the season. Removal of either parent did not influencethe growth of the young, although growth varied over the breeding season,and it was significantly different between the sites. Theseresults suggest that the payoff from parental care decreasesover the breeding season and that the value of parental care(i.e., the contribution of parents to the survival of theiryoung) may depend on the environment.     

Brood predation pressure during parental care does not influence parental enzyme activities related to swimming activity in a teleost fish

Predation is considered one of the main costs to reproduction but is rarely examined from a physiological perspective. In particular, little is known about the influence of brood predation pressure on the physiology of parents engaged in care. Brood defense, even when there is no direct threat to the parent, can be costly as it requires constant vigilance and chasing predators to protect the developing brood and maintain parental investment (i.e., fitness). Our goal was to examine the influence of natural variation in nest predation pressure on the physiology of the teleost smallmouth bass Micropterus dolomieu, an animal that provides sole-paternal care for developing offspring. More specifically, we used indicators of anaerobic (lactate dehydrogenase [LDH]) and aerobic capacity (cytochrome c oxidase [CCO] and citrate synthase [CS]) in axial white muscle and pectoral red muscle to test for differences in antipredator performance of nest guarding males across six lakes with natural variation in nest predation pressure. Pectoral red muscle enzyme activities and protein concentrations were highly conserved among populations, while axial white muscle showed differences in LDH activities, CCO activities and protein concentrations. However, there was no evidence for higher metabolic capacities in fish from lakes with increased brood predation pressure. Clearly, factors other than predation pressure have a greater influence on white muscle metabolic capacities. Additional research is needed to clarify the extent to which biotic and abiotic factors influence the enzyme activity and organismal performance in wild animals, particularly at the level of the individual and population.     

Male parental care, female reproductive success, and extrapair paternity

Birds differ considerably in the degree of male parental care,and it has been suggested that interspecific variation in extrapairpaternity is determined by the relative importance of benefitsto females from male parental care and good genes from extrapairsires. I estimated the relationship between extrapair paternityand the importance of male parental care for female reproductivesuccess mainly based on male removal studies, using a comparativeapproach. The reduction in female reproductive success causedby the absence of a male mate was positively correlated withthe male contribution to feeding offspring. The frequency ofextrapair paternity was negatively related to the reductionin female reproductive success caused by the absence of a mate.This was also the case when potentially confounding variablessuch as developmental mode of offspring and sexual dichromatismwere considered. A high frequency of extrapair paternity occursparticularly in bird species in which males play a minor rolein offspring provisioning and in which attractive males providerelatively little parental care. Bird species with frequentextrapair paternity thus appear to be those in which directfitness benefits from male care are small, females can readilycompensate for the absence of male care, and indirect fitnessbenefits from extrapair sires are important.     

Brood care in a Silurian ostracod

An exceptionally preserved new ostracod crustacean from the Silurian of Herefordshire, England, preserves eggs and possible juveniles within its carapace, providing an unequivocal and unique view of parental brood care in the invertebrate fossil record. The female fossil is assigned to a new family and superfamily of myodocopids based on its soft-part anatomy. It demonstrates a remarkably conserved egg-brooding reproductive strategy within these ostracods over 425 Myr. The soft-tissue anatomy urges extreme caution in classifying 'straight-hinged' Palaeozoic ostracods based on the carapace alone and fundamentally questions the nature of the shell-based Palaeozoic ostracod record.     

Task allocation in ant colonies within variable environments (A study of temporal polyethism: Experimental)

We briefly review the literature on the division of labour in ant colonies with monomorphic worker populations, and show that there are anomalies in current theories and in the interpretation of existing data sets. Most ant colonies are likely to be in unstable situations and therefore we doubt if an age-based division of labour can be sufficiently flexible. We present data for a type of small ant colony in a highly seasonal environment, concentrating on individually marked older workers. We show that contrary to expectation such workers undertake a wide variety of tasks and can even retain their ability to reproduce, even whilst younger workers are actively foraging. Our analysis shows that old workers occupy four distinct spatial stations within the nest and that these are related to the tasks they perform. We suggest that correlations between age and task in many ant colonies might simply be based on ants foraging for work, i.e. actively seeking tasks to perform and remaining faithful to these as long as they are profitably employed. For this reason, employed older workers effectively displace unemployed younger workers into other tasks. In a companion paper, Tofts 1993,Bull. math. Biol. develops an algorithm that shows how foraging for work can be an efficient and flexible mechanism for the division of labour in social insects. The algorithm creates a correlation between age and task purely as a by-product of itsmodus operandi.     

Brood insurance via protogyny: a source of female-biased sex allocation

Sex allocation patterns and colony productivity are examined in Exoneura nigrescens, a social allodapine bee. As for previous studies on Australian allodapine bees, numerical sex ratios were strongly female biased in the smallest broods, but neared equality in larger broods. Local fitness enhancement has been suggested previously to explain female-biased allocation in allodapine bees. Here, we propose an alternative model, the 'insurance model', which predicts protogyny and, as a consequence, female-biased sex allocation in small broods with decreasing bias in larger broods. Because allodapine broods are reared progressively in an open burrow, broods require that adult females be present throughout their development in order to survive to maturity. If mothers invest in daughters (alloparents) first, these daughters can rear younger, dependent brood in cases in which orphaning occurs. If such daughters behave as surrogate mothers, then investment in them by mothers should not be regarded as investment in female sex allocation per se, giving rise to apparently female-biased broods. The model predicts a pattern of sex ratios as a function of total brood size that very closely match empirical data from E. nigrescens.     

The evolutionary puzzle of egg size,oxygenation and parental care in aquatic environments

Offspring fitness generally improves with increasing egg size. Yet, eggs of most aquatic organisms are small. A common but largely untested assumption is that larger embryos require more oxygen than they can acquire through diffusion via the egg surface, constraining egg size evolution. However, we found no detrimental effects of large egg size on embryo growth and survival under hypoxic conditions. We tested this in the broad-nosed pipefish, Syngnathus typhle, whose males provide extensive care (nourishment, osmoregulation and oxygenation) to their young in a brood pouch on their bodies. We took advantage of this species'' pronounced variation in egg size, correlating positively with female size, and tested the effect of hypoxia (40% dissolved oxygen) versus fully oxygenated (100%) water on embryo size and survival of large versus small eggs after 18 days of paternal brooding. Egg size did not affect embryo survival, regardless of O₂ treatment. While hypoxia affected embryo size negatively, both large and small eggs showed similar reductions in growth. Males in hypoxia ventilated more and males with large eggs swam more, but neither treatment affected their position in the water column. Overall, our results call into question the most common explanation for constrained egg size evolution in aquatic environments.     

Brood care and social evolution in termites

Cooperative brood care is assumed to be the common driving factor leading to sociality. While this seems to be true for social Hymenoptera and many cooperatively breeding vertebrates, the importance of brood care for the evolution of eusociality in termites is unclear. A first step in elucidating this problem is an assessment of the ancestral condition in termites. We investigated this by determining the overall level of brood care behaviour across four termite species that cover the phylogenetic diversity of the lower termites. Brood care was low in the three species (all from different families) that had an ancestral wood-dwelling lifestyle of living in a single piece of wood that serves as food and shelter. In the fourth species, a lower termite that evolved outside foraging, brood care was more common. Together with data for higher termites, this suggests that brood care in termites only becomes important when switching from a wood-dwelling to a foraging lifestyle. These results imply that early social evolution in termites was driven by benefits of increased defence, while eusociality in Hymenoptera and cooperative breeding in birds and mammals are primarily based on brood care.     

Elasticities in variable environments: properties and implications

Elasticities in stochastic matrix models are used to understand both population and evolutionary dynamics. We examine three such elasticities: stochastic elasticity E(ij)(S) with respect to the (i, j) matrix element, the elasticity E(ij)(S mu) with respect to the mean mu(ij) of the matrix element, and the elasticity E(ij)(S sigma) with respect to the variability sigma(ij) of the matrix element. We show that the stochastic elasticity E(S) does not accurately describe the effect of variability; one should use E(S sigma) and E(S mu). We establish two general properties of these elasticities: a sum rule that connects them and a limit on the sum of the E(S sigma). We discuss the implications of these properties for the analysis of buffering and selection on the average rates versus the variability of rates.     

Adaptive management in variable environments

Adaptive management (AM) encourages land managers to modify plans for the future based on carefully evaluating what happened in the past. Extreme abiotic variation overwhelms effects of management, making AM extremely difficult to implement. We demonstrate how passive AM, involving monitoring over a few years and using data to inform future decisions, was used to determine seeding rates of native plants in a restoration experiment conducted in the Irvine Ranch National Landmark in Southern California. We found that seedling density depended more on the year in which seeding was conducted than on seeding rates. Analysis of longer term data, using weather as independent variables in analyses, can help managers tease apart the relative importance of management actions and of precipitation. Seeding in multiple years provided a bet hedging strategy for increasing success of the restoration project, given inter-annual variation in precipitation. Limitations of our seeding rate example could be resolved through active AM, in the form of controlled, manipulative experiments testing different seeding rates and replicated over many years. Effective AM requires a willingness to repeat management actions that failed due to abiotic conditions in a single year. What failed last year may work well in the future, and evaluating the role of environmental variation requires repetition across multiple years.

     

Coevolution in temporally variable environments

Many potentially mutualistic interactions are conditional, with selection that varies between mutualism and antagonism over space and time. We develop a genetic model of temporally variable coevolution that incorporates stochastic fluctuations between mutualism and antagonism. We use this model to determine conditions necessary for the coevolution of matching traits between a host and a conditional mutualist. Using an analytical approximation, we show that matching traits will coevolve when the geometric mean interaction is mutualistic. When this condition does not hold, polymorphism and trait mismatching are maintained, and coevolutionary cycles may result. Numerical simulations verify this prediction and suggest that it remains robust in the presence of temporal autocorrelation. These results are compared with those from spatial models with unrestricted movement. The comparisons demonstrate that gene flow is unnecessary for generating empirical patterns predicted by the geographic mosaic theory of coevolution.     

Breeding success, nestling diet and parental care in the White-backed WoodpeckerDendrocopos leucotos

In western Norway, pairs of White-backed Woodpecker breeding in coastal areas (<2 km from the sea) started egg laying earlier than pairs in inland areas (2–15 km from the sea). Laying was earlier in years when the ambient temperature was higher during the pre-laying period. About half of 69 pairs studied started laying within the period 25–30 April over the 10 study years. Clutch size ( = 4.0 eggs) and breeding success values (fledglings per egg; = 0.63) did not differ between years. The mean number of fledglings per nest was 2.4. The mean body mass of fledglings differed between years and were negatively correlated with the laying date. Fledgling mass differed between sexes (males = 87.8g, females = 84.2g), and both sexes were heavier in coastal than in inland areas. The mean hourly feeding rate of nestlings increased with nestling age, but feeding rate per nestling did not vary with nestling number. The nestling food was mainly comprised by wood-living beetle larvae ( = 72% by dry mass). It is suggested that breeding success is related to territorial quality, which, in turn, strongly influences female quality.

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Zusammenfassung In Westnorwegen beginnen Weißrückenspechte, die an der Küste brüten, eher mit der Eiablage als Paare im Inland (>2 km von der Küsten entfernt). Höhere Lufttemperaturen in der Vorlegezeit begünstigten frühere Eiablage. Mehr als die Hälfte der 69 untersuchten Paare begannen innerhalb von 10 Jahren zwischen 25. und 30. April mit der Eiablage. Gelegegröße ( = 4,0 Eier) und Bruterfolg (flügge Junge pro Ei; = 0,63) unterschieden sich nicht in einzelnen Jahren. Pro Nest flogen 2,4 Junge aus. Die mittlere Körpermasse der flüggen Jungvögel war mit dem Datum der Eiablage negativ korreliert. Flügge Männchen waren etwas schwerer als gleichalte Weibchen ( 87,9, 84,2 g); beide Geschlechter waren in Küstengebieten schwerer als im Inland. Die mittlere Fütterungsrate pro Stunde stieg mit dem Alter der Nestlinge, veränderte sich aber nicht mit der Zahl der Nestlinge. Die Nestlingsnahrung bestand vor allem aus holzbewohnenden Käferlarven ( = 72% der Trockenmasse). Vermutlich hängt der Bruterfolg mit der Qualität des Brutreviers zusammen, die wiederum vor allem die Kondition des Weibchens bestimmt.

     

Clupeoid life-history styles in variable environments

Synopsis Marine fish species with planktonic larval stages experience high and variable pre-adult mortality, and in accordance with general life-history theory have evolved iteroparity to reduce the uncertainty in reproductive success of individuals. In this paper we use a Monte Carlo model to explore the influence of spawning style and adult survival of clupeoids on the spawning success of individual fish during their life span, when early stage survival is determined according to different spectra of environmental variability. In these simulations the variation in reproductive success was governed first by the number of batches of eggs spawned by each adult fish over its lifespan (as determined by its pattern of spawning and the adult survival rate), and secondly by the patterning of environmental variability affecting early stage survival. We consider that the life history styles of the clupeoids are based on co-evolved traits in which the different patterns of iteroparity represent different solutions for coping with the variable nature of early-stage survival. When these life history traits are compared on time scales appropriate to each species, they are therefore unlikely to provide the correlation between brood strength variation and the life span of adults proposed in Murphy's (1968) contribution to this aspect of life history theory.     

Brood defence and parental roles in a biparental cichlid fishLamprologus toae in Lake Tanganyika

Brood defence of a cichlid fish,Lamprologus toae, was investigated in its natural habitat in Lake Tanganyika. Both parents guarding a brood attacked both conspecific and heterospecific intruder fishes at different locations. The heterospecific intruder fishes could be classified into three groups on the basis of the locations at which the attacks against each species took place. The distinction of groups by the parents seemed to be primarily based on food habits and feeding behaviour of the intruder fishes. The piscivorous species which were more dangerous for the brood were attacked by both parents at more distant locations from the brood. Parental defence of breeding territory changed with the development of the young. The frequency of attacks against each group decreased after the young reached the size too large for the fishes of the group to prey on. Division of labour in the territorial defence was recognized between male and female. The male parent mainly defended the peripheral region of the territory and the female parent defended the inner region. Significance of the selective attack against intruders and the division of labour between the two sexes in brood defence is discussed.     

Population dynamics in variable environments. VI. Cyclical environments

This paper studies the dynamics of an age-structured population which experiences cyclical variation in vital rates. The principal features of population behavior are found to be contained in an explicitly calculable response function. Three distinct regimes of qualitative behavior are described when cycle period is respectively much less than, of the order of, and much greater than the average generation length. These results make explicit the way in which transient properties corresponding to average vital rates determine population response to cycles.     

Relative reproductive success of female moorhens using conditional strategies of brood parasitism and parental care

In a population of moorhens (Gallinula chloropus), at least27% of netting females laid one or more eggs in a neighbor'snest Females laid parasitically under three conditions: 56%of parasitic eggs were from nesting females that preceded layinga dutch in their own nest by a parasitic laying bout, 19% werefrom females whose nests were depredated before clutch completionand that laid the following egg parasiticaDy, and 25% were froma small number of females without territories, "non-nesting"parasites, that each laid a series of parasitic eggs. Clutchsizes varied greatly between females, but nesting females eachlaid a consistent clutch size both within and between seasonsfor a given mate and territory. Nesting females that employeda dual strategy of brood parasitism and parental care producedextra eggs that they laid in the nests of neighbors before layinga dutch in their own nests. Two out of ten females whose dutchesI experimentally removed during the laying period were successfullyinduced to lay their next egg in the nest of a neighbor. Nestingfemales that laid parasitically selected their hosts opportunisticallyfrom among the nests dosest to their territories. An experimentin which parasitic eggs were removed and hosts left to rearonly their own young showed that parasites did not choose hoststhat were better parents than pairs with contemporary neststhat were not parasitized. Females that only laid parasiticaDywithin a given season timed their parasitic laying bouts poorlyand achieved no reproductive success. Parasitic young rarelyfledged, and the mean seasonal reproductive success of nestingbrood parasites did not differ from that of nonparasitic females.However, the variance in reproductive success of nesting broodparasites was significantly higher than that of nonparasiticfemales.     

Independent and competing disease risks: implications for host populations in variable environments

Disease models usually assume disease to act independently of other mortality- and morbidity-causing factors. Alternatively, disease may function as a competing risk factor, for example, killing already moribund hosts. Using tuberculosis (TB) in African buffalo as a model system, we explore consequences of competing or independent disease effects for host population dynamics. We include scenarios with density-dependent and density-independent effects of environmental variation, exemplified by variable food availability (driven by rainfall) and catastrophic droughts, respectively. Independent disease effects reduce population size linearly with prevalence, irrespective of the nature of environmental variation. Competing disease risks alter population size only if density-independent variation is present; then, disease reduces population size nonlinearly. Field data indicate that the net effect of TB on buffalo likely falls between the extremes of total independence and competition with other risk factors: TB increases mortality and decreases fecundity in some prime-aged buffalo, suggesting independent disease risks in these individuals, while similar disease effects in senescent buffalo may act as competing risks. Moreover, increased survival and fecundity of TB-negative buffalo may compensate for some disease-related losses. Model assumptions on independent or competing disease risks and environmental variability should be considered explicitly when assessing disease effects on wildlife populations.