Shoaling preference and evidence for maintenance of sibling groups by juvenile black perch Embiotoca jacksoni

Group sizes in free‐living juvenile black perch Embiotoca jacksoni were quantified and predictions of the hypothesis that such groups comprise sibling brood‐mates were tested. Group sizes in the field were within the range of female brood sizes and often occurred close to each other but did not merge. In captivity, juveniles formed groups immediately after birth. In laboratory experiments, they also associated significantly more with chambers containing familiar members of their own brood than empty chambers but did not associate more with chambers containing similar‐sized juveniles from a different brood. Juvenile E. jacksoni also associated significantly more with chambers containing familiar brood‐mates than with chambers containing unfamiliar members of a different brood. The strength of this preference increased with the number of days fish had been together since birth. When two broods were placed in a large outdoor tank, all individuals from both broods directed significantly more aggressive acts towards members of the other brood than towards members of their own brood. While the relative effects of familiarity and relatedness cannot be completely separated in this viviparous species, associating with familiar individuals would facilitate the maintenance of sibling groups in the field.     

Nest Enlargement in Leaf-Cutting Ants: Relocated Brood and Fungus Trigger the Excavation of New Chambers

During colony growth, leaf-cutting ants enlarge their nests by excavating tunnels and chambers housing their fungus gardens and brood. Workers are expected to excavate new nest chambers at locations across the soil profile that offer suitable environmental conditions for brood and fungus rearing. It is an open question whether new chambers are excavated in advance, or will emerge around brood or fungus initially relocated to a suitable site in a previously-excavated tunnel. In the laboratory, we investigated the mechanisms underlying the excavation of new nest chambers in the leaf-cutting ant Acromyrmex lundi. Specifically, we asked whether workers relocate brood and fungus to suitable nest locations, and to what extent the relocated items trigger the excavation of a nest chamber and influence its shape. When brood and fungus were exposed to unfavorable environmental conditions, either low temperatures or low humidity, both were relocated, but ants clearly preferred to relocate the brood first. Workers relocated fungus to places containing brood, demonstrating that subsequent fungus relocation spatially follows the brood deposition. In addition, more ants aggregated at sites containing brood. When presented with a choice between two otherwise identical digging sites, but one containing brood, ants'' excavation activity was higher at this site, and the shape of the excavated cavity was more rounded and chamber-like. The presence of fungus also led to the excavation of rounder shapes, with higher excavation activity at the site that also contained brood. We argue that during colony growth, workers preferentially relocate brood to suitable locations along a tunnel, and that relocated brood spatially guides fungus relocation and leads to increased digging activity around them. We suggest that nest chambers are not excavated in advance, but emerge through a self-organized process resulting from the aggregation of workers and their density-dependent digging behavior around the relocated brood and fungus.     

An analysis of the nesting behaviour of Geotrupes spiniger Marsham (Coleoptera, Scarabaeidae)

Abstract. 1. Female G.spiniger adults working alone made nests each consisting of a vertical shaft leading to a series of horizontal brood chambers filled with dung brood masses. Oviposition near the tip of the brood mass occurred while the egg cell was being completed over the expanded ovipositor. The shaft above each brood mass was filled with soil excavated from the next brood chamber. A similar response also filled artificial diverticula. An avoidance reaction towards buried dung prevented damage to pre-existing brood masses. 2. Virgin females did not make nests and did not avoid buried dung, but after mating (at about 4 weeks after eclosion) both types of behaviour were released within a few hours. 3. The presence of dung was required to initiate but not to maintain nesting behaviour. If dung was removed after oviposition the chamber was filled with soil produced by renewed excavation. Cellulose pulp could substitute for dung in brood mass formation. 4. Beetles interchanged between burrows at different stages before oviposition readily repeated all pre-oviposition behaviour. They appeared to respond to the length of the shaft and of the brood chamber since they extended short shafts and short brood chambers considerably more than those of normal length. After oviposition the beetles continued to make brood masses even under abnormal conditions. 5. Tilting the cage through 90° caused beetles before oviposition to re-orientate their burrowing direction, but tilting just after oviposition caused them to make vertical brood masses. Placing the shaft in a horizontal position towards the end of brood mass formation postponed the termination of this phase. 6. Beetles repeatedly excavated shafts and chambers when transferred to new cages. Conversely they repeatedly made brood masses when maintained in preformed plaster-of-Paris burrows. 7. This nesting behaviour can be described as a reaction chain in which each action generates its own terminating stimulus and initiates the subsequent response. The behaviour before oviposition could be omitted or repeated as required by the environment, but after oviposition there was little response to external interference. These characteristics have direct relevance to the survival of the larvae.     

Molecular genetic perspectives on avian brood parasitism

Advances in molecular genetic techniques have provided new approachesfor addressing evolutionary questions about brood parasiticbirds. We review recent studies that apply genetic data to thesystematics, population biology, and social systems of avianbrood parasites and suggest directions for future research.Recent molecular systematics studies indicate that obligatebrood parasitism has evolved independently in seven differentavian lineages, a tally that has increased by one in cuckoos(Cuculiformes) and decreased by one in passeriforms (Passeriformes)as compared to conventional taxonomy. Genetic parentage analysessuggest that brood parasitic birds are less promiscuous thanmight be expected given their lack of nesting and parental carebehavior. Host-specificity in brood parasites, which has importantimplications for host-parasite coevolution, has been evaluatedusing both population genetic and parentage analyses. Femalelineages are faithful to particular host species over evolutionarilysignificant time scales in both common cuckoos (Cuculus canorus)and indigobirds (Vidua spp.), but differences in the host-specificityof male parasites has resulted in different patterns of diversificationin these two lineages. Future research on brood parasitism willbenefit from the availability of comprehensive molecular phylogeniesfor brood parasites and their hosts and from advances in functionalgenomics.     

Should I stay or should I go? Female brood desertion and male counterstrategy in rock sparrows

Brood desertion involves a series of interactions between themembers of a pair. This process is likely to be based on eithermember's perception of the other's propensity to desert. Wemanipulated this perception in males by experimentally increasingfemale body mass in the rock sparrow (Petronia petronia), aspecies in which females can desert their first brood beforethe nestlings from the first brood leave the nest. We predictedthat the male would either desert the brood first or stay evenif this implied the risk of caring for the brood alone. We foundthat males mated to loaded females did not leave but stayedand significantly increased their courtship rate and mate guarding.Unexpectedly, they also increased their food provisioning tothe nestlings, even though loaded females did not reduce theirnestling-feeding rate. The increase in male feeding rate maybe explained as a way for the male to reduce the female's propensityto switch mate and desert or to increase her propensity to copulatewith the male to obtain paternity in her next brood. Altogether,our results demonstrate that the perception of the risk of beingdeserted by the female does not necessarily induce males todesert first, contrary to what is generally assumed by theoreticalmodels.     

Energy expenditure, nestling age, and brood size: an experimental study of parental behavior in the great tit Parus major

A brood manipulation experiment on great tits Parus major was performedto study the effects of nestling age and brood size on parentalcare and offspring survival. Daily energy expenditure (DEE)of females feeding nestlings of 6 and 12 days of age was measuredusing the doubly-labeled water technique. Females adjusted theirbrooding behavior to the age of the young. The data are consistentwith the idea that brooding behavior was determined primarilyby the thermoregulatory requirements of the brood. Female DEEdid not differ with nestling age; when differences in body masswere controlled for, it was lower during the brooding periodthan later. In enlarged broods, both parents showed significantlyhigher rates of food provisioning to the brood. Female DEE wasaffected by brood size manipulation, and it did not level offwith brood size. There was no significant effect of nestlingage on the relation between DEE and manipulation. Birds wereable to raise a larger brood than the natural brood size, althoughlarger broods suffered from increased nestling mortality ratesduring the peak demand period of the nestlings. Offspring conditionat fledging was negatively affected by brood size manipulation,but recruitment rate per brood was positively related to broodsize, suggesting that the optimal brood size exceeds the naturalbrood size in this population.     

Brood defense and brood size in the great tit (Parus major): a test of a model of unshared parental investment

To understand the interaction of the many contextual variablesthat affect parental behavior a number of static optimalitymodels have been developed. Among these the one by Lazarus andInglis (1986) is the only one to specifically predict the magnitudeof unshared parental investment (PI), i.e., of parental carethat carries a cost to the parent and that benefits all currentoffspring equally because it cannot be divided among them. Weinvestigated specifically how parent great tits (Parus major)gear their brood defense, a form of unshared PI, to the sizeof the brood at stake and to the risk incurred as a functionof the type of predator. The predators used were dummies ofthe great spotted woodpecker (Picoides major) and of the tawnyowl (Strix aluco). Normally, adults can approach the woodpeckerwith impunity; it had inflicted heavy losses to nestlings ofthe study populations of great tits near Wolfsburg, Lower Saxony.Parent great tits whose brood had been artificially reducedto two young responded to the dummy with less defense than dida control group with their pre-test brood size left intact.The nature of defense was qualitatively the same as that elicitedby a live woodpecker. Parents confronting the owl near theirbrood decreased their response with an artificial reductionin brood size much less. Because the owl used poses a seriousrisk to the defenders, as compared to the woodpecker, the resultlends powerful support to the "total loss" version of the modelof unshared PI; it predicts brood size to affect unshared PImore strongly when there is less risk to the parent. This interpretationis correct to the extent that one premise of the model, namelythat of uncompromised parentage, can be relaxed; great tit broodscontain a sizeable number of extrapair young. Males defendedtheir brood more strongly than did females. Sex and brood manipulationadded up linearly when affecting defense level, i.e., therewas no interaction.     

Antagonistic antiparasite defenses: nest defense and egg rejection in the magpie host of the great spotted cuckoo

Brood parasites dramatically reduce the reproductive successof their hosts, which therefore have developed defenses againstbrood parasites. The first line of defense is protecting thenest against adult parasites. When the parasite has successfullyparasitized a host nest, some hosts are able to recognize andreject the eggs of the brood parasite, which constitutes the secondline of defense. Both defense tactics are costly and would be counteractedby brood parasites. While a failure in nest defense implies successfulparasitism and therefore great reduction of reproductive successof hosts, a host that recognizes parasitic eggs has the opportunityto reduce the effect of parasitism by removing the parasiticegg. We hypothesized that, when nest defense is counteractedby the brood parasite, hosts that recognize cuckoo eggs shoulddefend their nests at a lower level than nonrecognizers becausethe former also recognize adult cuckoos. Magpie (Pica pica) hoststhat rejected model eggs of the brood parasitic great spottedcuckoo (Clamator glandarius) showed lower levels of nest defensewhen exposed to a great spotted cuckoo than when exposed toa nest predator (a carrion crow Corvus corone). Moreover, magpiesrejecting cuckoo eggs showed lower levels of nest defense againstgreat spotted cuckoos than nonrecognizer magpies, whereas differencesin levels of defense disappeared when exposed to a carrion crow.These results suggest that hosts specialize in antiparasitedefense and that different kinds of defense are antagonistically expressed.We suggest that nest-defense mechanisms are ancestral, whereasegg recognition and rejection is a subsequent stage in the coevolutionaryprocess. However, host recognition ability will not be expressedwhen brood parasites break this second line of defense.     

Brood care in the dung beetle Onthophagus vacca (Coleoptera: Scarabaeidae): the effect of soil moisture on time budget, nest structure, and reproductive success

Under laboratory conditions brood care behaviour, nest structure and weight of dung supply in brood chambers of the dung beetle Onthophagus vcca proved to depend on water content of the soil beneath the dung. The substrate in a bucket beneath the dung pat was dry sand (4% water content) or moist sand (8% water content). Emigrating beetles were trapped and counted at 12 h intervals. In a total of 109 replicates one pair was released on an artificial 1000 g dung pat. From 95 replicates in which brood chambers were built the following results were derived: 1) Breeding females and resident males which helped the female stayed longer in dung pats on dry sand than in those on moist sand. 2) Nest architecture was influenced by substrate moisture: length of main tunnels did not differ between nests in dry and moist sand, but total length of side tunnels was shorter in dry sand. 3) Numbers of brood chambers were equal in both substrate types, weight of the dung supplies was larger in dry sand. 4) Offspring size was not only influenced by dung provision in the brood chambers. Beetles emerging from chambers in dry sand were smaller than those emerging from moist sand even if the amount of dung supply was equal.     

The effect of partial brood loss on male desertion in a cichlid fish: an experimental test

There is little experimental evidence testing whether currentbrood size and past brood mortality influence mate desertion.In the cichlid Aequidens coeruleopunctatus both parents initiallydefend offspring. In a field study, all experimental broods,irrespective of initial brood size (222.9 ± 60.4, mean± SD), were manipulated to a size of 100 fry. Neitherthe duration nor investment of females in parental care differed between control and brood reduced pairs, even though care seemedcostly. On average, females lost 5.1 ± 4.8% of initialweight while guarding a brood until independence. In contrast,males with experimentally reduced broods guarded fry for significantlyfewer days before deserting their mate than did males fromcontrol pairs with natural-sized broods (20.5 ± 7.5 vs. 14.2 ± 6.2 days). In at least 20% of cases (n = 9/45),the deserting male immediately mated with another female. Maleswith experimentally reduced broods also spent less time guardingfry before deserting and attacked fewer brood predators thandid males with control broods. For broods manipulated to have100 fry, there was a significant negative relationship betweenthe days until male desertion and the proportion of the initialbrood removed. This indicates that male assessment of the futuresuccess of the current brood (hence its reproductive value)is based on past mortality and/or that there is variation amongmales in the expected size of future broods. Both current broodsize and brood size relative to initial brood size are thereforepredictors of male, but not female, parental behavior and matedesertion. Female care may be unaffected by brood reductiondue to limited breeding opportunities and partial compensationfor reduced male care.     

Hatching asynchrony, nestling competition, and the cost of interspecific brood parasitism

All parental hosts of heterospecific brood parasites must paythe cost of rearing non-kin. Previous research on nest parasitismby brown-headed cowbirds (Molothrus ater) concluded that competitivesuperiority of the typically more intensively begging and largercowbird chick leads to preferential feeding by foster parentsand causes a reduction in the hosts' own brood. The larger sizeof cowbird nestlings can be the result of at least two causes:(1) cowbirds preferentially parasitize species with smallernestlings and lower growth rates; and/or (2) cowbirds hatchearlier than hosts. I estimated the cost of cowbird parasitismfor each of 29 species by calculating the difference betweenhosts' published brood sizes in nonparasitized and parasitizednests and using clutch size to standardize values. In this analysis,greater incubation length and lower adult mass, surrogate measuresof the hatching asynchrony and size difference between parasiteand hosts, were both related to greater costs of cowbird parasitismwithout bias owing to phylogeny. To establish causality, I manipulatedclutch contents of eastern phoebes (Sayornis phoebe) and examinedwhether earlier hatching by a single cowbird or phoebe egg reducesthe size of the rest of the original host brood. As predicted,greater hatching asynchrony increased the proportion of theoriginal phoebe brood that was lost. This measure of the costof parasitism was partially owing to increased hatching failureof the original eggs in asynchronous broods but was not at allrelated to the size differences of older and younger conspecificnestmates. However, proportional brood loss owing to an earlierhatching conspecific was consistently smaller than brood lossowing to asynchronous cowbirds in both naturally and experimentallyparasitized phoebe nests. These results imply that althoughhatching asynchrony is an important cause of the reduction ofhost broods in parasitized clutches, competitive features ofcowbird nestlings remain necessary to explain the full extentof hosts' reproductive costs caused by interspecific brood parasitism.     

Sexual conflict among polygynous pied flycatchers feeding young

In the polygynous pied flycatcher, Ficedula hypoleuca, reproductivesuccess of females is constrained by male food provisioningduring the nestling period. Hence, there will be conflictinginterests among the male and each of his mates as to how malefeeding effort should be shared among broods. This paper describesthree experiments designed to examine the parental behaviorof the members of a bigynous trio, i.e., the male and his twomates, in light of these conflicts. In all experiments, primaryand secondary broods were manipulated to hatch on the same dayto reduce the difference in brood-reproductive value due toage. Males divided their effort equally when the two broodswere the same size. However, males did not allocate their investmentin proportion to brood size when brood sizes differed, but investedmore heavily per young in the larger broods. This finding suggeststhat males tried to optimize the joint effort of their two mates.Males and females showed similar responses to experimental reductionin brood demands, which indicates no difference in their willingnessto invest in offspring. When one of the male’s mates wasremoved temporarily, the male increased his total feeding rateand provided proportionately more food to the "motherless" brood.Through flexible allocation of parental investment, males seemable to optimize their reproductive interests in the two broods.The only way a polygynously mated female might successfullyincrease the amount of male assistance at her nest is to makeher own brood more valuable for the male, relative to the otherbroods he might have. We discuss some ways this might be achieved.[Behav Ecol 1991;2:106–115]     

THE SYSTEMATIC POSITION OF LAROCHEA FINLAY, 1927, AND INTRODUCTION OF A NEW GENUS AND TWO NEW SPECIES (GASTROPODA: SCISSURELLIDAE)

Species of the gastropod genus Larochea Finlay, 1927 are shownto be scissurellids without an anal shell slit or foramen. TheNew Zealand species, L. miranda Finlay, 1927 and L. secundaPowell, 1937, brood their young in the right subpallial cavityagainst a modified inner lip that is set well behind the aperturalplane. Larochea scitula n.sp. is based on shells from WanganellaBank, southern Norfolk Ridge. Larocheopsis n. gen. is introducedfor a minute species from off northern New Zealand that lacksa shell brood chamber. Larochea miranda and Larocheopsis amplexan.sp. are either gonochoristic with smaller males or consecutivehermaphrodites, while Larochea secunda and L. scitula are evidentlygonochoristic, having mature males and females of similar size. (Received 23 July 1992; accepted 10 December 1992)     

Clutch size and body size at first reproduction in Daphnia pulicaria at different levels of food and predation

Field data from seven alpine lakes in Serra da Estrela. Portugal.show that reproduction in Daphnia may be as efficiently controlledby fish predation and copepod predation on eggs in brood cavitiesas it is by food limitation. Body length and clutch size estimatesin Daphnia pulicaria revealed high inter- and intra-populationvariability in maturation size (body size at first reproduction).and in number of eggs per clutch. Daphnia at first maturationin lakes stocked with rainbow trout were half the size of thosefound in fishless lakes (body length of 0.86–0.95 and1.55–1.81 mm. respectively). The mean number of eggs perclutch was reduced to a similar degree by food limitation, predationby fish and copepod predation on eggs in brood cavities, butthe underlying mechanisms of this reduction were different.Food limitation caused smaller clutch sizes in all individuals,so variation remained the same. Fish predation caused the selectiveremoval of individuals with maximum clutches, so variation decreased.Copepod predation caused removal of eggs from brood cavitiesof randomly infested females, so that variation increased, particularlyat a high food level when non-infested females carried largeclutches of eggs.     

Duration and benefits of biparental brood care in the dung beetle Onthophagus vacca (Coleoptera: Scarabaeidae)

Abstract.

• 1 Single males, single females or pairs of dung beetles, Onthophagus vacca, were released on artificial small (100 g) or large (1000 g) dung pats in the laboratory. Emigrating beetles were trapped at 12 h intervals, and the number and size of the brood chambers were recorded after each replicate.
• 2 Emigration of males was delayed if females were present in the same dung pats, whereas emigration times of females were independent of the presence or absence of males.
• 3 A residency of 60 h proved to be a threshold value. Females emigrating before this time did not breed, whereas those emigrating later had built at least two brood chambers.
• 4 Females paired with males built more brood chambers than single females.
• 5 The reproductive success of pairs was not influenced by the size of the dung pats.

     

Nest construction and larval behaviour of Onitis belial and Onitis ion (Coleoptera, Scarabaeidae)

Abstract. 1. Female beetles working alone or in cooperation with a male buried dung to make brood masses. O.belial brood masses were packed close together in clusters; each mass was constructed as a horizontal thick-walled tube of dung which was filled with a dung sausage containing two to six eggs. O.ion made vertical sausage-shaped brood masses with one to four eggs.
2. The larvae of both species were able to survive in artificial brood balls as well as in multi-egg brood masses because of their ability to repair larval chambers with their own excrement.
3. The multi-egg brood mass of Onitis has probably evolved from a simple one-egg brood mass. It does not resemble the underground dung mass from which brood balls are made by certain Coprini.     

Brood parasitism by cowbirds: risks and effects on reproductive success and survival in indigo buntings

We observed brood parasitism by brown-beaded cowbirds (Molothrusater) on indigo buntings (Passerina cyanea) and estimated dieimpact of parasitism on the success of the individual buntingsin their current nests and in their future survival and reproduction.Rates of parasitism over 8 years were 26.6% in 1040 nests and19.8% in 693 nests in two areas in southern Michigan. Risk ofparasitism was high early in the season; half the bunting nestswere begun after the end of the cowbird season. Risk was independentof female age, plant containing the nest, or habitat The immediatecost of parasitism was 1.19 and 1.26 fewer buntings fledgedper nest. Bunting success was lower in parasitized nests withcowbird eggs (nests were more likely to be deserted or predated),lower when the cowbird nestling failed (nests were more likelyto be predated), and lower when the cowbird fledged (fewer buntingsfledged) compared to nonparasitized nests. Costs were due toremoval of a bunting egg when die cowbird laid its own egg andto competition for parental care of the cowbird and buntingnestlings. Buntings that fledged from nests where a cowbirdalso fledged were only 18% as likely to survive and return totheir natal area in the next year as buntings from nests wherea cowbird did not fledge. Long-term effects of cowbird parasitismon adult breeding later in the season, survival to the nextseason, and reproductive success in the next season were negligiblewhen compared between birds that reared a cowbird and birdsthat reared only a bunting brood, or between birds that wereparasitized and birds that escaped parasitism. The results indicatelittle long-term cost of brood parasitism on individual fitnessof adult buntings beyond the impact on the current nest andthe survival of buntings that fledge from it; nearly all costis to the parasitized brood.     

Intraspecific brood mixing and reduced polyandry in a maternal mouth-brooding cichlid

Microsatellite loci were used to evaluate the level of polyandryand intraspecific brood mixing in Protomelas c.f. spilopterus,a paedophagous, maternal mouth-brooding cichlid from Lake MakaiAfrica. We found that broods were fertilized by one to threemales, which was a reduced level of multiple paternity comparedto other mouth-brooding cichlids. Low density of breeding malesand the risk of intraspecific predation are likely explanationsfor reduced polyandry. Intraspecific brood-mixing was foundin four out of the six broods examined, with the proportionsof foreign fry ranging from 6% to 65%. The potential originsof brood mixing are discussed, although no firm conclusionscan be drawn given the limited behavioral observations for thisspecies.     

Strong evidence for selection for larger brood size in a great tit population

We measured the selection pressure on brood size in a recentlyestablished population of great tits (Parus major L.) in thenorthern Netherlands by manipulating brood size in three years(1995: n = 51, 1997: n = 66, 1998: n = 51), and we estimatedfitness consequences in terms of local survival of both offspringand parents. Enlarged broods had highest fitness; the offspringfitness component was positively affected by manipulation andthe parental fitness component was unaffected. Parental survivaland the probability that parents produced a second clutch werenot affected by the treatment. However, parents that had raisedenlarged broods produced their second clutch later in the season.Clutch size, brood size, and laying date of birds recapturedin the next breeding season were largely independent of thetreatment. We conclude that there is strong evidence for selectionfor larger brood size and reject the individual optimizationhypothesis for this population because the number of young inthe nest predicts fitness independently of the manipulationhistory.     

Brood size and begging intensity in nestling birds

Theoretical models suggest that sibling competition should selectfor conspicuous begging signals. If so, begging intensity mightbe expected to increase with the number of competitiors. Thepurpose of our study was to examine the relationship betweenbegging intensity and brood size using nestling tree swallows(Tachycineta bicolor) as our model. Over 2 years, we videotapedbegging behavior in unmanipulated broods of different sizes.We found that begging intensity increased with brood size. Theaverage weight of nestlings in each brood did not vary withbrood size, but feeding rate per nestling decreased with broodsize, suggesting that nestlings in larger broods begged moreintensively, possibly because they were hungrier. We also conductedan experiment to examine the effect of nest mates on beggingin different-sized broods. We found that nestlings with similarweights, previous competitive environments, and food deprivationbegged more intensively in large broods than in small broods.Overall, our study indicates that begging intensity increaseswith brood size in tree swallows. This relationship may resultfrom interactions among brood mates rather than from lower feeding rates to individual nestlings in larger broods.