HATCHING ASYNCHRONY IN ALTRICIAL BIRDS

1. The review aims to provide a simple conceptual framework on which to place recent studies of hatching asynchrony in altricial birds and to assess the evidence used in support of specific hypotheses. 2. Hatching asynchrony arises bsecause parents start incubation before laying is complete, but the precision of parental control is largely unknown. 3. Hypothesses concerning the functional significance of hatching asynchrony fall into four broad types. Hatching asynchrony might: (i) arise because of selection on the timing of events during the nesting period; (ii) facilitate the adaptive reduction in brood size; (iii) increase the energetic efficiency of raising the brood, or (iv) result from environmental or phylogenetic constraints. 4. The incubation pattern could function to minimize the losses of eggs, nestlings or adults to predators (or climatic sources of mortality), particularly in species which cannot actively defend their nest. The best evidence comes from comparative studies of hatching asynchrony. Early incubation might also be favoured if the food supply declines sharply through the breeding season, although the evidence is weak and indirect, or if there is a risk of brood parasitism. In species in which only the female incubates, early incubation could ‘force’ the male to invest more in the nestlings, but this idea remains to be tested. Males may be constrained by the risk of cuckoldry to delay incubation until laying is complete. 5. Hatching asynchrony could be adaptive by enabling the efficient reduction of brood size if food proves short after hatching (primarily because of a shortage of food in the environment or possibly because of a large proportion of ‘expensive’ nestlings in the brood in species which are sexually dimorphic). Observational evidence is often consistent with this hypothesis but few experimental studies provide adequate tests. Brood reduction could be adaptive in species (primarily eagles and pelecaniformes) which lay an extra egg to act as insurance against hatching failure, and again hatching asynchrony might facilitate brood reduction, although there are few experimental tests on such species. Hatching asynchrony might also enable sex ratio manipulation through selective brood reduction, although there is as yet no clear supportive evidence. 6. Ins species in which young have a marked peak in energy demand during the period of parental care, hatching asynchrony can reduce the peak demand of the brood, which might allow the parents to raise more healthy young. In many species such savings are likely to be small or absent. There is some behavioural evidence that hatching asynchrony can reduce fighting amongst nestlings and therefore lead to the more efficient use of energy by the brood. In general this effect seems small and the only energetic study found no difference in the energy requirements of synchronous and asynchronous broods. Other possible energetic advantages to hatching asynchrony have not been tested. 7. Environmental conditions during laying can influence both egg size and laying interval in aerial insectivores, and might directly influence incubation in this and other groups. Thus some variation in hatching asynchrony and the relative size of siblings is probably non-adaptive. The variability of incubation pattern within and across species suggests that hatching asynchrony is not under strong phylogenetic constraint. 8. The hypotheses about the adaptive significance of hatching asynchrony are complementary rather than mutually exclusive: within a species, several selective pressures could influence the optimal incubation pattern, and the relative importance of selective pressures will differ among species. Furthermore one should expect that the incubation pattern and parent–offspring interactions will be coadapted to maximize brood productivity.     

Forest snail faunas from Georgian Transcaucasia: patterns of diversity in a Pleistocene refugium

Thirty forest sites in Georgia were sampled to obtain inventories of their land snail faunas. The sites, in nine sampling areas, ranged from Batumi near the Turkish border to Lagodekhi near the Azerbaijan border, and included parts of both the Lesser and Greater Caucasus mountains and the Colchic lowlands. Abundance was generally low, and most sites held less than 20 species. Ninety species were found overall. Although sites within some sampling areas had very similar faunas, the overall levels of similarity among sites and sampling areas was low, especially when compared with similar forests from northern central Europe. Both climate and geographical position affected similarity: although these were correlated, independent effects of each were detected, and the effect of position alone was strongest. Despite this effect, most species have ranges extending into Turkey or Ciscaucasia, a few have very limited ranges, and there is no evidence of patterns of allopatric replacement among congeners. These patterns resemble those seen in faunas from forests in lower latitudes, and suggest a slow build‐up of regional diversity by differentiation in situ, without the repeated restrictions to a multiplicity of small refugia that are characteristic of areas where fluctuations in aridity are important. The refugium has remained isolated, and has contributed little to the Holocene recolonization of areas further north. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 239–250.     

A cryptic contact zone between divergent mitochondrial DNA lineages in southwestern North America supports past introgressive hybridization in the yellow‐rumped warbler complex (Aves: Dendroica coronata)

Using genetic data to study the process of population divergence is central to understanding speciation, yet distinguishing between recent divergence and introgressive hybridization is challenging. In a previous study on the phylogeography of the yellow‐rumped warbler complex using mitochondrial (mt)DNA data, we reported limited sequence divergence and a lack of reciprocal monophyly between myrtle and Audubon's warblers (Dendroica coronata and Dendroica auduboni, respectively), suggesting very recent isolation. In the present study, we report the results obtained from a subsequent sampling of Audubon's warbler in Arizona and Utah (‘memorabilis’ race), which shows that, although this taxon is similar to auduboni in plumage colour, most memorabilis individuals sampled (93%) carry haplotypes that belong to the divergent black‐fronted warbler lineage (Dendroica nigrifrons) of Mexico. Furthermore, the auduboni and nigrifrons lineages mix in southern Utah at a narrow, yet apparently ‘cryptic’ contact zone. Newly‐available evidence from nuclear markers indicating marked differentiation between auduboni and coronata has focused attention on the possibility of mtDNA introgression in the absence of nuclear gene flow, and the results of the present study are consistent with the hypothesis that the mtDNA of auduboni was indeed historically introgressed from the coronata lineage. Analysis of morphological traits shows that memorabilis is significantly differentiated from auduboni and nigrifrons in some traits, yet is overall intermediate between the two, which is consistent with a shared common ancestor for the auduboni/memorabilis/nigrifrons group. The striking, unexpected mtDNA pattern reported in the present study reveals a complex evolutionary history of the yellow‐rumped warbler complex, and cautions against the exclusive use of mtDNA to infer evolutionary relationships. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 696–706.     

Elevational trends in butterfly phenology: implications for species responses to climate change

1. Impacts of global change on the distribution, abundance, and phenology of species have been widely documented. In particular, recent climate change has led to widespread changes in animal and plant seasonality, leading to debate about its potential to cause phenological mismatches among interacting taxa. 2. In mountainous regions, populations of many species show pronounced phenological gradients over short geographic distances, presenting the opportunity to test for effects of climate on phenology, independent of variation in confounding factors such as photoperiod. 3. Here we show for 32 butterfly species sampled for five years over a 1700 m gradient (560–2260 m) in a Mediterranean mountain range that, on average, annual flight period is delayed with elevation by 15–22 days per kilometre. Species mainly occurring at low elevations in the region, and to some extent those flying earlier in the year, showed phenological delays of 23–36 days per kilometre, whereas the flight periods of species that occupy high elevations, or fly in late summer, were consistently more synchronised over the elevation gradient. 4. Elevational patterns in phenology appear to reflect a narrowing phenological window of opportunity for larval and adult butterfly activity of high elevation and late‐flying species. 5. Here, we speculate as to the causes of these patterns, and the consequences for our ability to predict species responses to climate change. Our results raise questions about the use of space–time substitutions in predicting phenological responses to climate change, since traits relating to flight period and environmental associations may influence the capacity of species to adapt to changing climates.     

The interpretation of hidden support in combined data phylogenetics

In phylogenetic analysis, support for a given clade is ‘hidden’ when isolated partitions support that clade less than in the analysis of combined data sets. In such simultaneous analyses, signal common to the majority of partitions dominates the topology at the expense of any signal idiosyncratic to each partition. This process is often referred to as synergy and is commonly used to validate the combination of disparate data partitions. We investigate the behaviour of hidden branch support (HBS), partitioned branch support (PBS) and hidden synapomorphy (HS) as measures of hidden support using artificial, real and experimentally manipulated phylogenetic data sets. Our analyses demonstrate that high levels of both HBS and HS can be obtained by combining data with little shared phylogenetic signal. This finding is in agreement with the original intent of hidden support metrics, which essentially quantify the extent of data set interaction, both through the dispersion of homoplasy and revelation of underlying shared signal (positive data synergy). High levels of HBS alone are insufficient to justify data combination. We advocate the use of multiple hidden support measures to distinguish between the dispersion of homoplasy and positive data synergy, and to better interpret data interactions. Furthermore, we suggest two criteria that help identify hidden support resulting from homoplasy dispersion: first, when total support decreases with the addition of a data partition and second, when total HBS per unit total support (TS) per node is similar to that derived from randomized data.     

Reproductive interactions of the Shiny Cowbird Molothrus bonariensis and the Yellow-hooded Blackbird Agelaius icterocephalus in Trinidad

The reproductive interactions of the Shiny Cowbird Molothrus bonariensis , a brood parasite, and the Yellow-hooded Blackbird Agelaius icterocephalus , a host of the cowbird, were studied In Trinidad, West Indies. We gathered information on the breeding biology of the Shiny Cowbird and the Yellow-hooded Blackbird, the frequency of use of the host species, and the effects of brood parasitism on host breeding success. Yellow-hooded Blackbirds are polygynous for the most part; males build nests and attempt to attract females to lay in them by means of song and visual displays directed towards the nests. This behaviour probably makes it easy for cowbirds to locate breeding birds and their nests. Cowbird eggs were found in 153 of 377 (40–3 %) blackbird nests located before the nestling stage. Shiny Cowbird parasitism of the Yellow-hooded Blackbird had little negative impact on host reproductive success, whereas predation accounted for the majority of nest failures. Vigilant nest defense by male blackbirds combined with colonial breeding apparently also minimized the extent of host egg damage and removal by cowbirds, and the parasitized and unparasitized nests were equally successful at producing blackbirds. Cowbirds most frequently parasitized the first or only nesting attempts in blackbird territories, and first or only nests were also successful more frequently than subsequent nests.     

An Examination of Scale-Dependent Resource Use by Eastern Hognose Snakes in Southcentral New Hampshire

ABSTRACT The decline of many snake populations is attributable to habitat loss, and knowledge of habitat use is critical to their conservation. Resource characteristics (e.g., relative availability of different habitat types, soils, and slopes) within a landscape are scale-dependent and may not be equal across multiple spatial scales. Thus, it is important to identify the relevant spatial scales at which resource selection occurs. We conducted a radiotelemetry study of eastern hognose snake (Heterodon platirhinos) home range size and resource use at different hierarchical spatial scales. We present the results for 8 snakes radiotracked during a 2-year study at New Boston Air Force Station (NBAFS) in southern New Hampshire, USA, where the species is listed by the state as endangered. Mean home range size (minimum convex polygon) at NBAFS (51.7 ± 14.7 ha) was similar to that reported in other parts of the species’ range. Radiotracked snakes exhibited different patterns of resource use at different spatial scales. At the landscape scale (selection of locations within the landscape), snakes overutilized old-field and forest edge habitats and underutilized forested habitats and wetlands relative to availability. At this scale, snakes also overutilized areas containing sandy loam soils and areas with lower slope (mean slope = 5.2% at snake locations vs. 6.7% at random locations). We failed to detect some of these patterns of resource use at the home range scale (i.e., within the home range). Our ability to detect resource selection by the snakes only at the landscape scale is likely the result of greater heterogeneity in macrohabitat features at the broader landscape scale. From a management perspective, future studies of habitat selection for rare species should include measurement of available habitat at spatial scales larger than the home range. We suggest that the maintenance of open early successional habitats as a component of forested landscapes will be critical for the persistence of eastern hognose snake populations in the northeastern United States.     

Cooperation within Actin Filament in Vertebrate Skeletal Muscle

When actin molecules form “rigor complexes” with nucleotide-free myosin, tropomn binds calcium with greater affinity and in a cooperative response the remaining actin molecules not cornplexed with myosin are “turned on” even though calcium is absent.     

The crustacean lacinia mobilis: a reconsideration of its origin, function and phylogenetic implications

The lacinia mobilis of the Crustacea Malacostraca is a more or less spine-like movable appendage of the medial mandibular edge, inserted near the base of the incisor process. It occurs in two or possibly three eumalacostracan superorders but is retained in the adult stage only in the Peracarida. The lacinia has been interpreted as the distal member of the spine-row found in many adult Malacostraca and/or their larvae, or alternatively as a derivative of a certain cusp ('cusp b') of the biting edge of the primitive lophogastrids. The distribution, ontogeny and function of the lacinia were studied in a variety of Eumalacostraca. There is great variability in the guiding and locking mechanisms involved in biting, within the subclass and even within single orders. A lacinia-based guiding and locking system is likely to function only in weak mandibles. New evidence is produced in favour of derivation of the lacinia from the spine-row, and the 'cusp b' derivation hypothesis is rejected, 'cusp b' being only a highly specialized lacinia. Doubt is cast upon the unity of the superorder Peracarida mainly because the place of the order Amphipoda within it is regarded as insecure.