Costs of growing up as a subordinate sibling are passed to the next generation in blue‐footed boobies

As stresses in early development may generate costs in adult life, sibling competition and conflict in infancy are expected to diminish the reproductive value of surviving low‐status members of broods and litters. We analysed delayed costs to blue‐footed booby fledglings, Sula nebouxii, of junior status in the brood, which involves aggressive subordination, food deprivation and elevated corticosterone, but little or no deficit in size at fledging. In ten cohorts observed for up to 16 years, juniors showed no deficit in breeding success at any age, independent of lifespan, including in a sample of sibling pairs. Among females, juniors actually outreproduced seniors across the 16‐year span. However, offspring produced by juniors in the first 3 years of life were less likely to recruit into the breeding population than offspring of seniors. Since junior fledglings survive, recruit and compete as well as seniors (shown earlier), and breed as successfully as seniors across the lifespan, it appears the delayed cost of subordination is passed to offspring, and only to those few offspring produced in the first 3 years of life. These correlational results indicate that systematic competition‐related differences in developmental conditions of infant siblings can alter their reproductive value by affecting the viability of their eventual offspring.     

Interrelations between early child development,gestational age and birth weight

Five traits of early child development were studied in 656 infants from the day of birth till 2 years of age. The infants selected for follow-up were born at 26–42 weeks of gestational age and with a birth weight accordingly ranging from 860 to 4560g. Analysis of variance was carried out for each of the following five traits which entailed the age at which a child: 1) turned himself over (turned); 2) sat unsupported for a few seconds (sat); 3) stood up (stood); 4) walked unsupported (walked); and 5) cut its first tooth (tooth). The results of this survey show no significant sex differences in the age of initial occurrence of any of the studied traits. Comparison with older siblings of the surveyed infants indicated a significant sibling resemblance component for all 5 trais, with the respective intraclass correlation coefficients ranging between 0.34 and 0.53. Gestational age and birth weight, but not “tooth”, appeared to be important messages of an infant's motor development, insofar as onset of the studied traits. The separate correlations of “turned”, “sat”, “stood” and “walked” with gestational age or weight were all negative and statistically highly significant. Research Unit — Human Population Biology, Division of Anatomy and Anthropology     

A new version of PRT software for sibling groups reconstruction with comments regarding several issues in the sibling reconstruction problem

Pedigree reconstruction using genotypic markers has become an important tool for the study of natural populations. The nonstandard nature of the underlying statistical problems has led to the necessity of developing specialized statistical and computational methods. In this article, a new version of pedigree reconstruction tools (PRT 2.0) is presented. The software implements algorithms proposed in Almudevar & Field (Journal of Agricultural Biological and Environmental Statistics, 4, 1999, 136) and Almudevar (Biometrics, 57, 2001a, 757) for the reconstruction of single generation sibling groups (SG). A wider range of enumeration algorithms is included, permitting improved computational performance. In particular, an iterative version of the algorithm designed for larger samples is included in a fully automated form. The new version also includes expanded simulation utilities, as well as extensive reporting, including half-sibling compatibility, parental genotype estimates and flagging of potential genotype errors. A number of alternative algorithms are described and demonstrated. A comparative discussion of the underlying methodologies is presented. Although important aspects of this problem remain open, we argue that a number of methodologies including maximum likelihood estimation (COLONY 1.2 and 2.0) and the set cover formulation (KINALYZER) exhibit undesirable properties in the sibling reconstruction problem. There is considerable evidence that large sets of individuals not genetically excluded as siblings can be inferred to be a true sibling group, but it is also true that unrelated individuals may be genetically compatible with a true sibling group by chance. Such individuals may be identified on a statistical basis. PRT 2.0, based on these sound statistical principles, is able to efficiently match or exceed the highest reported accuracy rates, particularly for larger SG. The new version is available at http://www.urmc.rochester.edu/biostat/people/faculty/almudevar.cfm.     

Sibling negotiation

Current discussions of offspring begging typically assume eitherthat it is a signal directed at parents or that it representsa form of scramble competition to gain access to them. However,offspring might also display to inform nest mates that theywill contest the next food item to be delivered; in other words,begging (possibly in the absence of parents) might serve purelyas a form of negotiation among siblings. Here, we develop agame-theoretical model of this possibility. We assume that offspringvary in their need for food, which influences how intenselythey compete for access to parents. Before parental arrival,however, young may exchange signals informing each other oftheir state, and these signals may influence their subsequentcompetitive behavior. We focus on the possibility that a costlydisplay during the "negotiation" phase can serve to inform rivalsof a chick's need for resources and thereby deter them fromcompeting intensely when the parent arrives. We show that thisform of negotiation is more likely to prove stable when thefood delivered by parents is indivisible, and when it is hardfor one chick to monopolize access to resources. Investmentin negotiation (as opposed to competition) is predicted to increasewith nestling relatedness; in addition, all other things beingequal, hungrier chicks are expected to invest relatively moreeffort in displaying to their rivals, whereas weaker or smallerchicks are expected to invest less.     

Games among cannibals: competition to cannibalize and parent-offspring conflict lead to increased sibling cannibalism

Sibling cannibalism occurs in many species, yet understanding of sibling cannibalism as an adaptation currently lags behind understanding of other antagonistic interactions among siblings. Observed sibling cannibalism phenotypes likely reflect the interaction between competitive games among siblings and parent-offspring conflict. Using a game-theoretic approach, we derive optimal offspring cannibalism behaviour and parental modifiers that limit or facilitate cannibalism. The results are compared to contemporary frequency-independent analysis. With the addition of game interactions among siblings or parent-offspring co-evolution, our model predicts increased cannibalism (compared to the frequency-independent prediction), as offspring compete to eat siblings. When infertile eggs are present--strengthening competition--offspring risk eating viable siblings in order to gain access to infertile eggs, intensifying parent-offspring conflict. We use the results to make new predictions about the occurrence of sibling cannibalism. Additionally, we demonstrate the utility of trophic egg laying as a maternal mechanism to promote egg eating.     

A simple and rapid technique for identification of large numbers of individual mosquitoes using DNA hybridization

A general method for obtaining species-specific repetitive DNA sequences is described. The method is based on the detection of recombinant DNA clones containing repetitive sequences using labeled total genomic DNA. These repetitive DNA sequences can be used to identify individual mosquito adults, pupae, and larvae squashed on filter membranes (squash blots). This technique was used to distinguish individuals of the four sibling species of the Anopheles quadrimaculatus complex. Repetitive DNA sequences and squash blots can be of use for rapid identification of other insect species in field collections.     

Genetic differentiation of disjunct populations of the antsFormica aquilonia andFormica lugubris in Europe

Summary The speciesFormica aquilonia andF. lugubris of the mound-building red wood ants have a disjunct boreoalpine distribution in Europe. The populations ofF. aquilonia in Finland, Switzerland and the British Isles show little genetic differentiation, whereas the populations ofF. lugubris show considerable differentiation. The Central European populations morphologically identified asF. lugubris can be genetically divided into two groups (here called types A and B). Type B is found in the Alps and the Jura mountains, and is genetically inseparable fromF. aquilonia. Type A lives sympatrically with type B in the Jura mountains and is also found in the British Isles. Sympatry of the two types in the Jura shows that these are separate species. It remains open whether type B is morphologically atypicalF. aquilonia or whether it is a separate species, perhaps with a past history of introgression betweenF. aquilonia andF. lugubris. The gene frequencies in the Finnish populations ofF. lugubris differ from those of both types A and B. Genetic differences withinF. lugubris indicate that the populations have evolved separately for a long time. The social structure ofF. lugubris colonies also shows geographic variation. The nests in Finland and the British Isles seem to be mainly monogynous and monodomous, whereas the nests in Central Europe are polygynous and form polydomous colonies.F. aquilonia has polygynous and polydomous colonies in all populations studied.     

Group provisioning limits sharing conflict among nestlings in joint-nesting Taiwan yuhinas

Offspring often compete over limited available resources. Such sibling competition may be detrimental to parents both because it entails wasted expenditure and because it allows stronger offspring to obtain a disproportionate share of resources. We studied nestling conflict over food and its resolution in a joint-nesting species of bird, the Taiwan yuhina (Yuhina brunneiceps). We show that adult yuhinas coordinate their feeding visits, and that this coordination limits competition among nestlings, leading to a ‘fairer’ division of resources. Transponder identification and video-recording systems were used to observe adult feeding and nestling begging behaviours. We found that: (i) yuhinas feed nestlings more often in large parties than in small parties; (ii) feeding events occurred non-randomly in bouts of very short intervals; and (iii) food distribution among nestlings was more evenly distributed, and fewer nestlings begged, during large-party feeding bouts compared with small-party feeding bouts. To our knowledge, this is the first study in a cooperative breeding species showing that adults can influence food allocation and competition among nestlings by coordinating their feeding visits. Our results confirm the hypothesis that the monopolizability of food affects the intensity of sibling competition, and highlight the importance of understanding the temporal strategies of food delivery.     

Parent-absent begging: evidence for sibling honesty and cooperation in the spotless starling (Sturnus unicolor)

Begging in avian nestlings is a highly conspicuous behaviorwith important implications for the study of parent–offspringconflict. In some species, nestlings also call for long boutsin the absence of parents, and it has been proposed that thisbehavior is used by nestlings as a means of negotiating accessto food. We studied this phenomenon in the spotless starling(Sturnus unicolor). We found that parent-absent calls were acousticallydistinct from parent-present calls. Observations showed thatthe probability of parent-absent begging increased with nestlingage and brood size, whereas it decreased with increasing bodycondition. This result was confirmed by an experiment that showedthat nestlings produced higher parent-absent begging rates whenfood deprived than when satiated. Finally, we carried out aplayback experiment to test the reaction of nestlings to parent-absentbegging by fellow nestlings. Principle components analyses yielded2 independent components of begging: 1) a general begging componentand 2) a second factor that measures the relative contributionof communicative begging over competitive begging. Nestlingsexposed to playback decreased their general begging levels andsimultaneously increased the relative contribution of communicativeover competitive begging. This behavior may favor needy nestlingsto obtain impending feedings while keeping high levels of foodsolicitation from parents and is consistent with a cooperativestrategy among nestlings. Future research should consider theactual response of parents to these signals.     

Life History of Ilybius fenestratus (Fabricius) (Coleoptera,Dytiscidae) in a Central Norwegian Lake

The life history of Ilybius fenestratus was studied in Målsj?en, a lake in S?r-Tr?ndelag, Central Norway (63°14'N, 10°26'E), during 1971–1972. Adults and larvae were sampled in activity traps every week during March–October and every 2–3 weeks during November–February. Newly-emerged adults were generally found from mid-July to September, and after overwintering in torpidity, probably in the water, they again appeared in the second half of June to August/September. Laying of eggs took place from early/mid July to early August. Larvae occurred in the traps from late July to early May. I. fenestratus was thus found to be a semivoltine summer breeder, with overwintering larvae the first winter and overwintering adults the next. Both adults and larvae lived in large areas of the lake's littoral zone.     

Sibship effects on dispersal behaviour in a pre‐industrial human population

Understanding dispersal behaviour and its determinants is critical for studies on life‐history maximizing strategies. Although many studies have investigated the causes of dispersal, few have focused on the importance of sibship, despite that sibling interactions are predicted to lead to intrafamilial differences in dispersal patterns. Using a large demographic data set from pre‐industrial Finland (n = 9000), we tested whether the sex‐specific probability of dispersal depended on the presence of same‐sex or opposite‐sex elder siblings who can both compete and cooperate in the family. Overall, following our predictions, the presence of same‐sex elder siblings increased the probability of dispersal from natal population for both sexes, whereas the number of opposite‐sex siblings had less influence. Among males, dispersal was strongly linked to access to land resources. Female dispersal was mainly associated with competition over availability of mates but likely mediated by competition over access to wealthy mates rather mate availability per se. Besides ecological constraints, sibling interactions are strongly linked with dispersal decisions and need to be better considered in the studies on the evolution of family dynamics and fitness maximizing strategies in humans and other species.     

Large Intercontinental Differentiation of Moina Micrura (Crustacea: Anomopoda): One Less Cosmopolitan Cladoceran?

Moina micrura Kurz, 1874 (Crustacea: Anomopoda), commonly regarded as a cosmopolitan cladoceran species, can be found almost all over the world except for arctic and cold-temperate regions. M. micrura has been recorded from virtually all types of limnetic habitats, including temperate permanent ponds, lakes, ephemeral desert pools, and tropical brackish fishponds. Its high morphological and ecological variability has so far been considered a result of intraspecific diversity. We tested the hypothesis that genetically isolated groups exist within M. micrura with crossing experiment and DNA sequence analysis. We compared two clones originating from populations from Central Europe (area of the type locality) and Australia. As there was extremely low production of hybrid eggs, the results of the crossing experiment strongly suggest the existence of reproductive isolation. The sequence divergence of mitochondrial gene for 12S rRNA (7.9%) was comparable to intraspecific differences within Daphnia pulex group. The sequence divergence of the clones of Moina macrocopa from Europe and Central Africa was much lower (1.4%). Our results suggest that at least two sibling species exist within M. micrura complex, which is in agreement with other data questioning the cosmopolitanism of various cladoceran species.     

Sex and rank in competitive brood hierarchies influence stress levels in nestlings of a sexually dimorphic bird

Studies of sibling competition within brood hierarchies have rarely assessed simultaneously the effects of sex and rank in the brood hierarchy on traits other than offspring mortality and differential growth. We studied the expression of heat-shock proteins (Hsps) to assess the physiological stress response to different combinations of sex and position within competitive brood hierarchies in the black kite Milvus migrans (Bodd.), a sexually dimorphic raptor showing facultative siblicide. Senior males showed higher stress levels than did senior females and younger siblings of each sex as revealed by Hsp60 values. The analysis of Hsp70 levels indicated that nestlings from broods in which the senior chick was a male showed higher stress levels than did nestlings from broods in which the senior chick was a female. In addition, levels of Hsp60 were related negatively to nutritional condition expressed as levels of plasmatic albumin. This suggests that the sex of senior chicks may be key in determining their stress level and that of their siblings, which is probably associated with sibling competition by fighting within brood hierarchies. The comparatively higher stress levels of senior males (and their siblings) may be a consequence of their ability to exploit their potential advantage from being the head start while avoiding a possible competitive disadvantage from being the smaller sex, independent of environmental conditions determining the probability of brood reduction. Differential stress levels depending on sex and rank in the brood hierarchy may be a consequence of parental control of offspring behaviour through differential resource allocation (e.g. yolk androgens) or it may reflect adaptations of particular chicks (senior males) to enhance their competitive ability within brood hierarchies.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 383–390.     

Higher gregarine parasitism often in sibling species of host damselflies with smaller geographical distributions

1. This study investigated inter‐specific variation in parasitism by gregarines (Eugregarinorida: Actinocephalidae), among sibling species of damselflies (Odonata: Zygoptera), in relation to relative size of geographical ranges of host species. 2. Gregarines are considered generalist parasites, particularly for taxonomically related host species collected at the same sites or area. Prevalence and median intensity of gregarine parasitism was obtained for 1338 adult damselflies, representing 14 species (7 sibling species pairs) across 3 families within the suborder Zygoptera. Damselflies were collected at three local sites in Southeastern Ontario, during the same periods over the season. 3. Five out of seven species pairs had significant differences in parasitism between sibling species. The less widespread host species was the more parasitised for three species pairs with significant differences in gregarine prevalence, and for two species pairs with differences in median intensity. The more widespread host had a higher intensity of infection as expected, in two species pairs. 4. Future studies on ecological determinants of parasitism among related species should examine robust measures of abundance of species and representation of species regionally.     

Identification of the sibling species of the Drosophila willistoni subgroup through the electrophoretical mobility of acid phosphatase-1

The Drosophila willistoni group consists of 23 species of which six are sibling species and belong to the D. willistoni subgroup: D. willistoni, Drosophila equinoxialis, Drosophila tropicalis, Drosophila insularis, Drosophila pavlovskiana and Drosophila paulistorum. These sibling species are abundant in the Neotropical region and can hardly be differentiated by the usual taxonomic traits. Four of them (D. willistoni, D. equinoxialis, D. tropicalis and D. paulistorum) cover extensive geographic distribution areas overlapping in places while two of them are endemic (D. insularis and D. pavlovskiana). In this study, we presented a method for the identification of five sibling species of the D. willistoni subgroup based on the allozyme variation of acid phosphatase‐1 (Acph‐1) in acrylamide gel electrophoresis. Our work showed that Acph‐1 allozyme differences can be used for species‐diagnostic characterization. This method was shown to be a more efficient tool for species identification than others because it is both quicker and produces reliable results.     

Morphological, cytogenetic and allozymic variation within Cephalofovea (Onychophora: Peripatopsidae) with descriptions of three new species

Variation within and between populations of Cephalofovea (Peripatopsidae) has been examined by allozyme, karyological and morphological analyses. Four groups are recognized on the basis of allozyme electrophoresis. One group includes specimens from the type locality of the only described species of the genus, C. tomahmontis. While karyotypic and morphological character states show considerable inter-group variation, the distributions of these states among groups are not concordant when different characters are compared. However, each group of populations is uniquely defined by the full suite of character states it possesses. The four groups are recognized here as distinct species with three species described as new.     

Molecular genetic analyses of species boundaries in the sea

The tools of molecular genetics have enormous potential for clarifying the nature and age of species boundaries in marine organisms. Below I summarize the genetic implications of various species concepts, and review the results of recent molecular genetic analyses of species boundaries in marine microbes, plants, invertebrates and vertebrates. Excessive lumping, rather than excessive splitting, characterizes the current systematic situation in many groups. Morphologically similar species are often quite distinct genetically, suggesting that conservative systematic traditions or morphological stasis may be involved. Some reproductively isolated taxa exhibit only small levels of genetic differentiation, however. In these cases, large population sizes, slow rates of molecular evolution, and relatively recent origins may contribute to the difficulty in finding fixed genetic markers associated with barriers to gene exchange. The extent to which hybridization blurs species boundaries of marine organisms remains a subject of real disagreement in some groups (e.g. corals). The ages of recently diverged species are largely unknown; many appear to be older than 3 million years, but snails and fishes provide several examples of more recent divergences. Increasingly sophisticated genetic analyses make it easier to distinguish allopatric taxa, but criteria for recognition at the species level are highly inconsistent across studies. Future molecular genetic analyses should help to resolve many of these issues, particularly if coupled with other biological and paleontological approaches.