Who is in the neighborhood? Conspecific and heterospecific responses to perceived density for breeding habitat selection

Theoretical models of habitat selection often incorporate negative density dependence. Despite strong negative density‐dependent effects on habitat selection, more recent studies indicate that animals settle near members of their own (conspecific) and other species (heterospecific) when selecting habitat with social cues. Social cue use for habitat selection is particularly common among songbirds, but few studies have investigated if songbirds use social cues to assess conspecific or heterospecific density (as opposed to just presence/absence) when making settlement decisions. We conducted a playback experiment to evaluate if yellow warblers (Setophaga petechia) and willow flycatchers (Empidonax traillii), two potential competitors for breeding habitat, use social cues to assess density (conspecific for warblers and heterospecific for flycatchers) when selecting breeding locations at two spatial scales. We simulated yellow warbler density to be high or low at multiple treatment plots (3.14 ha) with song playback and then evaluated settlement decisions by comparing yellow warbler and willow flycatcher abundances across plots (broad‐scale habitat selection) and individual space use within plots (fine‐scale territory establishment). Yellow warbler density treatments did not affect habitat selection by yellow warblers at the broad scale, but caused individuals to cluster territories at high‐density treatments. Willow flycatchers were most abundant at high‐density treatment plots, but yellow warbler density treatments did not affect territory locations. The results indicate that perceived density affects the habitat selection process for both conspecifics and heterospecifics.     

Genetic and morphological diversity of mouse lemurs (Microcebus spp.) in northern Madagascar: The discovery of a putative new species?

Tropical forests harbor extremely high levels of biological diversity and are quickly disappearing. Despite the increasingly recognized high rate of habitat loss, it is expected that new species will be discovered as more effort is put to document tropical biodiversity. Exploring under‐studied regions is particularly urgent if we consider the rapid changes in habitat due to anthropogenic activities. Madagascar is known for its extraordinary biological diversity and endemicity. It is also threatened by habitat loss and fragmentation. It holds more than 100 endemic primate species (lemurs). Among these, Microcebus (mouse lemurs) is one of the more diverse genera. We sampled mouse lemurs from several sites across northern Madagascar, including forests never sampled before. We obtained morphological data from 99 Microcebus individuals; we extracted DNA from tissue samples of 42 individuals and amplified two mitochondrial loci (cytb and cox2) commonly used for species identification. Our findings update the distribution of three species (Microcebus tavaratra, Microcebus arnholdi, and Microcebus mamiratra), including a major increase in the distribution area of M. arnholdi. We also report the discovery of a new Microcebus lineage genetically related to M. arnholdi. Several complementary approaches suggest that the newly identified Microcebus lineage might correspond to a new putative species, to be confirmed or rejected with additional data. In addition, morphological analyses showed (a) clear phenotypic differences between M. tavaratra and M. arnholdi, but no clear differences between the new Microcebus lineage and the sister species M. arnholdi; and (b) a significant correlation between climatic variables and morphology, suggesting a possible relationship between species identity, morphology, and environment. By integrating morphological, climatic, genetic, and spatial data of two northern Microcebus species, we show that the spatial distribution of forest‐dwelling species may be used as a proxy to reconstruct the past spatial changes in forest cover and vegetation type.     

Prebasic molt initiation and progress in northern fulmars of the High Arctic: do molt and breeding overlap?

We examined feather molt progress of northern fulmars (Fulmarus glacialis) at Cape Vera in the Canadian High Arctic through opportunistic observation of individuals in flight from 2003 to 2006, and examination of bodies and wings of 127 individuals collected at the site, from 2003 to 2005. We found no evidence suggesting that fulmars shed primary feathers during breeding. Prebasic molt was initiated in the head, neck, sides, belly and back approximately 1 week before hatch. We failed to detect a sex effect on molt progress, but molt among breeders was delayed compared to molt in non- or failed breeders. This study constitutes a baseline we feel may be useful to: (1) researchers interested in feather replacement chronology, wherein feathers are used as sources of biological information; and (2) researchers interested in eventual assessment of relationships among large-scale environmental processes and molt progress in this species, especially in light of predicted changes to Arctic regions.     

Density dependence of avian clutch size in resident and migrant species: is there a constraint on the predictability of competitor density?

The presence of density dependence of clutch size is tested in 57 long-term population studies of 10 passerine bird species. In about half of the studies of tit species Parus spp. density dependence of clutch size was found, while none was found in studies of two flycatcher species Ficedula spp. One hypothesis explaining this difference is that migrants are less able to predict the final competitor density, because new pairs are still settling when the first females start laying eggs. Such unpredictability is only a problem for early laying females. If this explanation is true, the commonly observed negative correlation between clutch size and laying date should be stronger in high-density years. I tested this prediction in three populations of Pied Flycatcher Ficedula hypoleuca , and compared the results with three populations of Great Tit Parus major . In none of the six populations was there a significant correlation between the strength of the seasonal decline in clutch size and population density. Thus the lack of density dependence of clutch size in Pied Flycatchers was not consistent with the idea that this is caused by the unpredictability of final density at the time of egg-laying of the earliest females in the population. Furthermore, density does not have any adverse effect on reproductive output of Pied Flycatchers, and therefore they do not adjust clutch size to density.     

Biogeography of avian blood parasites (Leucocytozoon spp.) in two resident hosts across Europe: phylogeographic structuring or the abundance–occupancy relationship?

Relationships between hosts and parasites represent complex co-evolving systems that can vary both temporally and spatially. This variation may result in different phylogeographic outcomes, ranging from highly geographically structured parasite populations comprised of specialist lineages that are locally abundant but have restricted global occupancy to geographically unstructured parasite populations consisting of widespread parasites. Here, we present results from a large biogeographic study of the Leucocytozoon blood parasites of two nonmigrant bird species, conducted at nine sites across Europe. The aim was to determine whether the parasite lineages of the two hosts were phylogeographically structured across Europe. Employing molecular methods, we found a large diversity of parasites, and although overall prevalence varied greatly, the parasites were not genetically structured. Several measures of local parasite abundance were associated with the number of sites that the lineage occurred in, which is consistent with the macroecological phenomenon of the abundance-occupancy relationship. Taken together, our results show that parasite dispersal is somewhat uncoupled to that of the host in this system: we suggest that broad host and/or vector preference may play an important role in determining the distribution of these parasites and in affecting host-parasite coevolution in this system.     

Trying to fit in: are patterns of orientation of a keystone grazer set by behavioural responses to ecosystem engineers or wave action?

The distribution of animals varies at different temporal and spatial scales. At the smallest scale, distribution may be orientated in regard to particular environmental variables or habitat features. For animals on the rocky intertidal, the processes which set and maintain patterns of distribution and abundance in wave-exposed areas are well studied, with explanatory models focused on wave action and, more recently, the role of biogenic habitats. In contrast, patterns of orientation by intertidal animals have received less attention, although having ecological and fitness consequences. Here, we report tests of competing models to explain the observation that limpets on steeply sloped surfaces orientate downwards. A greater proportion of downwards-facing limpets was found in sheltered sites and areas without barnacles and this pattern was consistent across many shores and sampling occasions. Additionally, the frequency at which limpets were dislodged after a storm was independent of orientation. To test whether orientation is a behavioural response to habitat-forming barnacles, barnacles were removed and/or killed from patches of substrata and the change in proportion of downwards-facing limpets measured. The proportion increased with barnacle removal and this behaviour was a response to the structure of the barnacles, not a biotic effect associated with the living organism. Our study suggests that biogenic habitat not wave action sets patterns of limpet orientation and barnacle shells, regardless of whether the barnacle is alive or not, limit the ability of limpets to adopt a downward orientation.     

Lack of mitochondrial genetic structure in hamlets (Hypoplectrus spp.): recent speciation or ongoing hybridization?

Species in the genus Hypoplectrus (hamlet fish) have been recognized primarily on the basis of colour morphology, which varies substantially. Limited differentiation in other morphological characters, however, has led to ongoing debate about their taxonomy. Our analysis of mtDNA sequences demonstrates neither reciprocal monophyly nor significant genetic differentiation among hamlet colour morphs. These data are potentially consistent with a model of recent speciation due to sexual selection on colour morphology. The presence within hamlets of two divergent mtDNA clades, however, suggests a longer history during which hybridization and gene flow have prevented the differentiation of hamlet colour morphs, at least in neutral genetic markers.     

Electrophysiological and behavioural responses of the housefly to “sweet” volatiles of the flowers of Caralluma europaea (Guss.) N.E. Br.

In sapromyiophilous plants, up to date, long range attraction of fly pollinators has been thoroughly investigated and attributed to “fetid” floral compounds, while the “sweet” floral scent fraction has not been specifically investigated and its role has received little attention. The aim of the present study was to verify if terpenoids, which are the main compounds of the floral bouquet of Caralluma europaea, play a role in the attraction of its pollinator Musca domestica. Terpinolene, α-terpinene and linalool, described as the three main volatiles of the flowers of C. europaea, were evaluated in electrophysiological investigations and blends of these compounds as well as the whole fresh flowers were used in behavioural assays. Antennae of housefly adults showed positive dose-dependent responses to all the chemicals tested. Houseflies were attracted by the odour of the fresh flowers and by the reconstructed terpenoid blend at the dose of 100 μg. At the dose of 10 μg, the blend did not produce any attraction. The results of the present study support the hypothesis that terpinolene, α-terpinene and linalool emitted by C. europaea flowers are involved in pollinator attraction and demonstrate the importance of the “sweet” scent in this sapromyiophilous species.     

Nile perch (Lates niloticus,L.) and cichlids (Haplochromis spp.) in Lake Victoria: could prey mortality promote invasion of its predator?

The invasion of Nile perch into Lake Victoria is one of the iconic examples of the destructive effect of an introduced species on an ecosystem but no convincing explanation exists of why Nile perch only increased dramatically after a 25 year lag. Here, we consider this problem using a mathematical model that takes into account interactions between Nile perch and its cichlid prey. We examined competing hypotheses to explain Nile perch invasion and show that suppression of juvenile Nile perch by cichlids may cause the system to have two alternative stable states: one with only cichlids and one with coexistence of cichlids and Nile perch. Without cichlid predation on Nile perch, alternative stable states did not occur. Our analysis indicates that cichlid mortality, for example fishing mortality, may have induced the observed shift between the states.     

Physiological responses of wheat and barley to Russian wheat aphid, Diuraphis noxia (Mordvilko) and bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae)

Although aphids are among the most injurious of all agronomic insect pests, much remains unknown about how their feeding alters plant physiology. Two experiments were conducted to examine the physiological responses of wheat, Triticum aestivum L. and barley, Hordeum vulgare L. to injury by Diuraphis noxia (Mordvilko) and Rhopalosiphum padi (L.) (Hemiptera: Aphididae). Gas-exchange parameters, chlorophyll fluorescence, and chlorophyll content were examined at 3, 6, and 9 days post-infestation on control and aphid (D. noxia and R. padi) infested treatments. In general, chlorophyll content and chlorophyll fluorescence parameters (non-variable minimal fluorescence, maximal fluorescence, and variable fluorescence) were not significantly affected by either aphid species. Photochemical and non-photochemical quenching coefficients were significantly impacted by both aphid species, suggesting that aphid feeding may influence the photoprotective xanthophyll cycle altering the thylakoid membrane pH gradient. Feeding by both aphid species resulted in an increase in electron transport rate, but at different time periods. Wheat plants infested with D. noxia had accelerated declines in photosynthetic capacity when compared to R. padi-infested and control plants. These plants exhibited decreased values for A_max, which was accompanied by decreased values for V_cmax and J_max Neither aphid species negatively affected the photosynthetic capacity of the barley plants until day 9. At this time, aphid-infested plants had decreased values for A_max which was accompanied by decreased values in J_max. Although R. padi feeding does not typically result in visual damage symptoms as previously demonstrated, clearly this aphid does have an impact on the gas-exchange and chlorophyll fluorescence of its host plants. Handling editor: Heikki Hokkanen     

Patterns of morphological changes and hybridization between sympatric whitefish morphs (Coregonus spp.) in a Swiss lake: a role for eutrophication?

Whitefish, genus Coregonus, show exceptional levels of phenotypic diversity with sympatric morphs occurring in numerous postglacial lakes in the northern hemisphere. Here, we studied the effects of human‐induced eutrophication on sympatric whitefish morphs in the Swiss lake, Lake Thun. In particular, we addressed the questions whether eutrophication (i) induced hybridization between two ecologically divergent summer‐spawning morphs through a loss of environmental heterogeneity, and (ii) induced rapid adaptive morphological changes through changes in the food web structure. Genetic analysis based on 11 microsatellite loci of 282 spawners revealed that the pelagic and the benthic morph represent highly distinct gene pools occurring at different relative proportions on all seven known spawning sites. Gill raker counts, a highly heritable trait, showed nearly discrete distributions for the two morphs. Multilocus genotypes characteristic of the pelagic morph had more gill rakers than genotypes characteristic of benthic morph. Using Bayesian methods, we found indications of recent but limited introgressive hybridization. Comparisons with historical gill raker data yielded median evolutionary rates of 0.24 haldanes and median selection intensities of 0.27 for this trait in both morphs for 1948–2004 suggesting rapid evolution through directional selection at this trait. However, phenotypic plasticity as an alternative explanation for this phenotypic change cannot be discarded. We hypothesize that both the temporal shifts in mean gill raker counts and the recent hybridization reflect responses to changes in the trophic state of the lake induced by pollution in the 1960s, which created novel selection pressures with respect to feeding niches and spawning site preferences.     

Isolation and phylogeny of novel cytochrome P450 genes from tunicates (Ciona spp.): a CYP3 line in early deuterostomes?

Cytochromes P450 (CYPs) form a gene superfamily involved in the biotransformation of numerous endogenous and exogenous natural and synthetic compounds. In humans, CYP3A4 is regarded as one of the most important CYPs due to its abundance in liver and its capacity to metabolize more than 50% of all clinically used drugs. It has been suggested that all CYP3s arose from a common ancestral gene lineage that diverged between 800 and 1100 million years ago, before the deuterostome-protostome split. While CYP3s are well known in mammals and have been described in lower vertebrates, they have not been reported in non-vertebrate deuterostomes. Members of the genus Ciona belong to the tunicates, whose lineage is thought to be the most basal among the chordates, and from which the vertebrate line diverged. Here we describe the cloning, exon-intron structure, phylogeny, and estimated expression of four novel genes from Ciona intestinalis. We also describe the gene structure and phylogeny of homologous genes in Ciona savignyi. Comparing these genes with other members of the CYP clan 3, show that the Ciona sequences bear remarkable similarity to vertebrate CYP3A genes, and may be an early deuterostome CYP3 line.     

The evolution of parental and alloparental effort in cooperatively breeding groups: when should helpers pay to stay?

We used a reproductive skew framework to consider the evolutionof parental and alloparental effort in cooperatively breedinggroups. The model provides the first theoretical treatmentof rent payment (the "pay-to-stay" hypothesis) for the evolutionof helping behavior of subordinates. According to this hypothesis,not all helping behavior is kin selected, but group membershelp in order to be allowed to stay in the group and potentiallygain breeding positions later in life. We show that reproductiveconcessions may be replaced by complete skew and voluntary,costly alloparental effort by subordinates once future prospectsare included in fitness calculations. This suggests that incompleteskew observed in long-lived species is not due to dominantcontrol over reproduction. Rent payment is predicted to occurwhen relatedness between subordinate and dominant is low, survivalis high, ecological constraints are at least moderately tight,and retaining nonhelping subordinates harms the dominant'sfitness. Rent may also be required from related subordinatesif helping is very costly (leading to low voluntary helpingeffort) and ecological constraints are moderately tight. However, related subordinates do not need to have a positive net effecton the dominant's direct fitness to be accepted as group members.We also consider compensatory responses of dominant group membersas a potential threat to the stability of renting behavior.If dominants trade off parental effort against their own survival,they may selfishly reduce their own parental effort as a responseto increased help. As this improves their own survival, theprospects of territorial inheritance diminish for the subordinate,and subordinates should hence be less willing to accept therent agreement. However, we show that compensatory responsesby "lazy" parents prevent group formation only in borderlinecases.     

The use of microsatellites to analyze relationships and to decipher homonyms and synonyms in Azorean apples (Malus?×?domestica Borkh.)

The objective of this study was to exploit the molecular and morphological variability present in Malus domestica to clarify the confused characterization of apple plantations in the Azores. Most Azorean apples are grown in orchards. They are usually given a local name, and sometimes the same name is used for different cultivars and varieties which share morphology and should be known by different names. Two-hundred samples of apples cultivated in the Azores were analyzed by use of ten microsatellites. The total number of alleles per locus ranged from 10 to 24, with a mean of 15.2. Heterozygosity was high, reflecting the high variability of the samples. Expected heterozygosity varied within a narrow range, from 0.74 to 0.88, whereas observed heterozygosity ranged from 0.41 to 0.98. The high genetic variability contributed to the high discriminating power, which ranged between 0.84 and 0.93. These microsatellites were used to unambiguously discriminate most of the tested apple cultivars on the basis of their allelic profiles. The rooted UPGMA tree organized most of the samples into thirteen main clusters, often with high bootstrap values. We identified 60 synonyms and 32 homonyms among the samples. Moreover, it was possible to relate each individual to its originating population and detect likely parent–offspring groups.     

Numerical increases and distributional shifts of Chrysaora quinquecirrha (Desor) and Aurelia aurita (Linné) (Cnidaria: Scyphozoa) in the northern Gulf of Mexico

Fisheries resource trawl survey data from the National Marine Fisheries Service from a 11–13-year period to 1997 were examined to quantify numerical and distributional changes of two species of northern Gulf of Mexico scyphomedusae: the Atlantic sea nettle, Chrysaora quinquecirrha (Desor), and the moon jelly, Aurelia aurita (Linné). Trawl surveys were grouped into 10 statistical regions from Mobile Bay, Alabama to the southern extent of Texas, and extended seaward to the shelf break. Records of summertime C. quinquecirrha medusa populations show both an overall numerical increase and a distributional expansion away from shore in the down-stream productivity field of two major river system outflows: Mobile Bay and the Mississippi-Atchafalaya Rivers. In addition, there is a significant overlap between summer C. quinquecirrha and lower water column hypoxia on the Louisiana shelf. In trawl surveys from the fall, A. aurita medusae showed significant trends of numerical increase in over half of the regions analyzed. For both species, there were statistical regions of no significant change, but there were no regions that showed significant decrease in number or distribution. The relationships between natural and human-induced (e.g. coastal eutrophication, fishing activity and hard substrate supplementation) ecosystem modifications are very complex in the Gulf of Mexico, and the potential impact of increased jellyfish populations in one of North America's most valuable fishing grounds is a most critical issue. Several hypotheses are developed and discussed to guide future research efforts in the Gulf of Mexico.     

Effects of habitat fragmentation on foraging behaviour of tits and related species: does niche space vary in relation to size and degree of isolation of forest fragments?

We studied the winter foraging niches of tits and related species in deciduous forest fragments varying in size between 1 and 30 ha (plus one forest of 200 ha) in order to investigate the influence of forest fragmentation on foraging niches Very few correlations between niche structure (foraging niche, width and overlap) and forest size or isolation turned out to be significant This implies that either the species that disappear in small fragments are those that suffer most from competition (making the effect unmeasurable), or that competition is relatively unimportant for niche structure In any case we find no evidence that foraging niches are strongly affected by the changes (in habitat and/or community structure) associated with fragmentation     

Discordance Between Spatial Distributions of Y-Chromosomal and Mitochondrial Haplotypes in African Green Monkeys (Chlorocebus spp.): A Result of Introgressive Hybridization or Cryptic Diversity?

Introgressive hybridization may cause substantial discordances among phylogenies based on different genetic markers. Such discordances have been found in diverse mammal species including primates. A recent study of mitochondrial DNA (mtDNA) revealed several poly- and paraphyletic relationships in African green monkeys (Chlorocebus), suggesting contemporary and/or ancient introgressive hybridization among almost all parapatric species of the genus. However, mtDNA analyses alone do not allow us to draw conclusions concerning introgression events. In this study we analyzed two Y chromosomal (Y-chr) markers for 30 African green monkey samples and compared the resulting genetic relationships to those based on published mtDNA data. In line with the results for mtDNA, we found no Y-chr evidence of hypothesized hybridization among Chlorocebus sabaeus and C. tantalus in the northern part of the contact zone in West Africa, and we found two distinct and distantly related Y-chr haplotypes within the range of C. tantalus, suggesting possible cryptic genetic diversity rather than ancient introgressive hybridization in this species. In contrast, Y-chr data revealed monophyletic relationships within Chlorocebus pygerythrus from East Africa, suggesting that mtDNA paraphylies found in this species are most likely to be the result of ancient introgressive hybridization and subsequent cytonuclear extinction of an earlier taxon. Our results accentuate the importance of analyzing sex chromosomal data in addition to mtDNA to obtain more information on the potential outcomes of hybridization with respect to genetic and species diversity. Analysis of more diverse nuclear marker sets is needed to obtain a more complete picture of the African green monkey evolution.     

Photosynthetic capacity and temperature responses of photosynthesis of rubber trees (Hevea brasiliensis Müll. Arg.) acclimate to changes in ambient temperatures

The aim of this study was to assess the temperature response of photosynthesis in rubber trees (Hevea brasiliensis Müll. Arg.) to provide data for process-based growth modeling, and to test whether photosynthetic capacity and temperature response of photosynthesis acclimates to changes in ambient temperature. Net CO₂ assimilation rate (A) was measured in rubber saplings grown in a nursery or in growth chambers at 18 and 28°C. The temperature response of A was measured from 9 to 45°C and the data were fitted to an empirical model. Photosynthetic capacity (maximal carboxylation rate, V _cmax, and maximal light driven electron flux, J _max) of plants acclimated to 18 and 28°C were estimated by fitting a biochemical photosynthesis model to the CO₂ response curves (A–C _i curves) at six temperatures: 15, 22, 28, 32, 36 and 40°C. The optimal temperature for A (T _opt) was much lower in plants grown at 18°C compared to 28°C and nursery. Net CO₂ assimilation rate at optimal temperature (A _opt), V _cmax and J _max at a reference temperature of 25°C (V _cmax25 and J _max25) as well as activation energy of V _cmax and J _max (E _aV and E _aJ) decreased in individuals acclimated to 18°C. The optimal temperature for V _cmax and J _max could not be clearly defined from our response curves, as they always were above 36°C and not far from 40°C. The ratio J _max25/V _cmax25 was larger in plants acclimated to 18°C. Less nitrogen was present and photosynthetic nitrogen use efficiency (V _cmax25/N _a) was smaller in leaves acclimated to 18°C. These results indicate that rubber saplings acclimated their photosynthetic characteristics in response to growth temperature, and that higher temperatures resulted in an enhanced photosynthetic capacity in the leaves, as well as larger activation energy for photosynthesis.     

Age structure, growth, mortality, and density of belugas (Delphinapterus leucas) in the Canadian Arctic: responses to environment?

Environmental constraints on life-history traits are expected to increase with seasonality in resources such as food and appropriate breeding habitat. Seasonality is highest at polar latitudes, where environmental constraints can be stronger than biotic factors, such as density and its effect on intraspecific competition. In this study, the age structure, body-length distribution, mortality, and density were studied and compared among five beluga populations of the Canadian Arctic: eastern Beaufort Sea (EBS), Baffin Bay (BB), Cumberland Sound (CS), western (WHB), and eastern Hudson (EHB) Bay, to test the prediction that density-dependent effects on these life-history traits should be inversely related to latitude. Growth, but not mortality, showed a significant positive relationship with latitude. Winter density also increased with winter latitude, consistent with the prediction of greater risk of mortality associated with density-independent effects, such as ice entrapment in winter. Age distributions differed among populations, with animals harvested at the highest-latitude population (EBS) being the oldest and attaining the longest adult body lengths, compared to lower-latitude populations (WHB and EHB). The latitudinal variation in growth, adult body size, and winter density is congruent with the hypothesis that environmental seasonality may impose stronger constraints on life-history traits of beluga with increasing latitude.