Quantified reproductive isolation in Heliconius butterflies: Implications for introgression and hybrid speciation

Heliconius butterflies have become a model for the study of speciation with gene flow. For adaptive introgression to take place, there must be incomplete barriers to gene exchange that allow interspecific hybridization and multiple generations of backcrossing. The recent publication of estimates of individual components of reproductive isolation between several species of butterflies in the Heliconius melpomene–H. cydno clade allowed us to calculate total reproductive isolation estimates for these species. According to these estimates, the butterflies are not as promiscuous as has been implied. Differences between species are maintained by intrinsic mechanisms, while reproductive isolation of geographical races within species is mainly due to allopatry. We discuss the implications of this strong isolation for basic aspects of the hybrid speciation with introgression hypothesis.     

Genetically effective population sizes of Antarctic seals estimated from nuclear genes

We analyzed eight nuclear microsatellite loci in three species of Antarctic seals; Weddell seal (Leptonychotes weddellii; mean N = 163), crabeater seal (Lobodon carcinophaga; 138) and Ross seal (Ommatophoca rossii; 35). We estimated genetic diversity (Θ) and effective population size (N _E) for each species. Autosomal microsatellite based N _E estimates were 151,200 for Weddell seals, 880,200 for crabeater seals, and 254,500 for Ross seals. We screened one X-linked microsatellite (Lw18), which yielded similar N _E estimates to the autosomal loci for all species except the Ross seals, where it was considerably larger (~103 times). Microsatellite N _E estimates were comparable with previously published N _E estimates from mitochondrial DNA, but both are substantially lower than direct estimates of population size in all species except the Ross seals. The ratio of maternally versus biparentally derived estimates of N _E for Ross seals was not consistent with the hypothesis that they are a polygynous species. We found no sign of a recent, sustained genetic bottleneck in any of the species.     

Measuring Ucrit and endurance: equipment choice influences estimates of fish swimming performance

This study compared the critical swimming speed (U_crit) and endurance performance of three Australian freshwater fish species in different swim‐test apparatus. Estimates of U_crit measured in a large recirculating flume were greater for all species compared with estimates from a smaller model of the same recirculating flume. Large differences were also observed for estimates of endurance swimming performance between these recirculating flumes and a free‐surface swim tunnel. Differences in estimates of performance may be attributable to variation in flow conditions within different types of swim chambers. Variation in estimates of swimming performance between different types of flumes complicates the application of laboratory‐based measures to the design of fish passage infrastructure.     

Length‐weight relationships of flatfish species caught by bottom trawl in the Yellow Sea and the Bohai Sea,China

This study determined the length–weight relationships of five flatfish species from the Yellow Sea and the Bohai Sea in China. Two of the species (Cynoglossus semilaevis and Verasper variegatus) had no previous length‐weight estimates.     

Estimating occupancy dynamics in an anuran assemblage from Louisiana,USA

Effective monitoring programs are designed to track changes in the distribution, occurrence, and abundance of species. We developed an extension of Royle and Kéry's (2007) single species model to estimate simultaneously temporal changes in probabilities of detection, occupancy, colonization, extinction, and species turnover using data on calling anuran amphibians, collected from 2002 to 2006 in the Lower Mississippi Alluvial Valley of Louisiana, USA. During our 5-year study, estimates of occurrence probabilities declined for all 12 species detected. These declines occurred primarily in conjunction with variation in estimates of local extinction probabilities (cajun chorus frog [Pseudacris fouquettei], spring peeper [P. crucifer], northern cricket frog [Acris crepitans], Cope's gray treefrog [Hyla chrysoscelis], green treefrog [H. cinerea], squirrel treefrog [H. squirella], southern leopard frog [Lithobates sphenocephalus], bronze frog [L. clamitans], American bullfrog [L. catesbeianus], and Fowler's toad [Anaxyrus fowleri]). For 2 species (eastern narrow-mouthed toad [Gastrophryne carolinensis] and Gulf Coast toad [Incilius nebulifer]), declines in occupancy appeared to be a consequence of both increased local extinction and decreased colonization events. The eastern narrow-mouthed toad experienced a 2.5-fold increase in estimates of occupancy in 2004, possibly because of the high amount of rainfall received during that year, along with a decrease in extinction and increase in colonization of new sites between 2003 and 2004. Our model can be incorporated into monitoring programs to estimate simultaneously the occupancy dynamics for multiple species that show similar responses to ecological conditions. It will likely be an important asset for those monitoring programs that employ the same methods to sample assemblages of ecologically similar species, including those that are rare. By combining information from multiple species to decrease the variance on estimates of individual species, our results are advantageous compared to single-species models. This feature enables managers and researchers to use an entire community, rather than just one species, as an ecological indicator in monitoring programs. © 2011 The Wildlife Society.     

Eight microsatellite markers for the San Esteban chuckwalla,Sauromalus varius

We characterize eight polymorphic microsatellite loci for the San Esteban chuckwalla, Sauromalus varius, which are being used as markers in a study of the genetic results from a decade of captive breeding in this endangered species. Observed heterozygosity estimates for S. varius ranged from 0.00 to 0.30, whereas expected heterozygosity estimates ranged from 0.06 to 0.58.     

The Rift Valley is a major barrier to dispersal of African clawed frogs (Xenopus) in Ethiopia

The Ethiopian highlands – home to striking species diversity and endemism – are bisected by the Rift Valley, a zone of tectonic divergence. Using molecular data we examined the evolutionary history of two co‐distributed species of African clawed frog (Xenopus clivii and X. largeni) that are endemic to this region. Our field collections substantially extend the known distribution of X. largeni, a species formerly known from highlands southeast of the Rift, but that also occurs to the northwest. In both species, analysis of mitochondrial DNA and 19 autosomal loci identifies significant population structure, suggests little or no recent migration across the Rift Valley, and provides divergence time estimates across the Rift of ～1–3.5 million years. These results indicate that the Ethiopian Rift Valley is a major obstacle to dispersal of highland‐adapted amphibians.     

Distribution,community structure and production of fishes in the upper Speed River,Ontario: a preimpoundment study

Synopsis The upper Speed River, on which a dam was under construction, was surveyed through fourteen qualitative and six quantitative collections to determine the distribution of fishes in the river above Guelph, Ontario and in a tributary, Luteral Creek. At the quantitative localities the removal method was used to estimate density and standing crop of all species. At three of these localities age and growth of the dominant species were determined and total ecological production calculated. Two approaches to the estimation of production for the 0–1 age class were compared and found to result in differences of 33–39% in the estimates of total production, thus illustrating the extent to which methodology may affect such estimates The dominant species in the river were, Semotilus atromaculatus, Notropis cornutus, Pimephales notatus, Rhinichthys atratulus, Hypentelium nigricans, Catostomus commersoni, Ambloplites rupestris, Micropterus dolomieui and Etheostoma flabellare. Density ranged from 11126 to 74765 individuals per hectare and standing crop from 32.4 to 190.0 kg ha⁻¹. Production values at the three localities were 15, 19 and 54 kg ha⁻¹ yr⁻¹ , and are low compared with estimates for other fluvial systems. Comparison with a 1951 survey of the Speed River revealed considerable changes in the composition and distribution of fish species. The ranges of several cold-water species had contracted towards the headwaters, whereas several warm-water species had extended their ranges up the river     

Conservation implications of low encounter rates of five nocturnal primate species (<Emphasis Type="Italic">Nycticebus </Emphasis>spp.) in Asia

Five species of slow lorises were once considered to comprise a single strongly polymorphic species, Nycticebus coucang, ranging throughout South and Southeast Asia. The cryptic nature of these nocturnal primates has led to a lack of understanding of their distribution patterns and abundance. In short surveys, often few if any lorises are detected, meaning that the few available density estimates are from long-term studies. Based on new research in Sebangau National Park, Borneo, and compilation of survey data from other areas, we provide the first comparative abundance estimates for all five slow loris species: N. coucang occurred in significantly higher abundances (median encounter rate 0.80/km: n = 15), than N. bengalensis (0.26/km; n = 12), or N. javanicus (0.11/km: n = 2), N. menagensis (0.02/km: n = 3), and N. pygmaeus (0.13/km: n = 4). Abundance estimates in Sebangau (0.19/km) did not increase with increasing survey effort, but for all species and studies combined, study duration was positively correlated with abundance estimates. We did not find a relation between abundance and body mass, nor between abundance and latitude. Long-term studies are more likely to be conducted at sites where the species of interest is particularly plentiful. The data suggest that slow lorises occur at low abundances throughout much of their range, and some in larger social groups than previously assumed. We recommend taking into account the species’ heterogeneous distribution (potentially requiring larger survey effort), their social structure, the use of red lights as opposed to white lights whilst surveying, and to make use of their vocalisations when surveying slow lorises.     

Estimating the phylogeny in mollusc Littorina saxatilis (Olivi) from enzyme data: methodological considerations

The evolutionary history of 19 populations of Littorina saxatilis (Olivi) was estimated by four different approaches. Three of these operate upon a population by population matrix of genetic distances: average linkage clustering, and two versions of the Fitch-Margoliash method. The fourth method was a maximum likelihood estimate based on differences in allele frequencies between populations. The study aims to assess how well each method estimates the phylogeny by including seven populations of the closely related species L. arcana Hannaford Ellis. The rationale behind this is that a good estimation technique should be able to separate these two monophyletic taxa.The results show that, by our criteria, the maximum likelihood method yields the best estimate and the unconstrained Fitch-Margoliash technique gives reasonable estimates. Both average-linkage clustering and the Fitch-Margoliash method with evolutionary clock perform less well. We argue that this is expected since both these techniques are based on probably unrealistic assumptions such as the overall rate of evolutionary divergence being homogeneous over phyletic lines.     

Global patterns in biomass models describing prey consumption by big cats

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Survival estimates of bird species across altered habitats in the tropical Andes

The probability of long‐term persistence of a population is strongly determined by adult survival rates, but estimates of survival are currently lacking for most species of birds in the tropical Andes, a global biodiversity hotspot. We calculated apparent survival rates of birds in the Ecuadorian tropical Andes using a moderately long‐term (11 yr) capture–recapture dataset from three habitats that varied in how much they had been modified by human activities (native forest, introduced forest, and shrubs). We fit mark–recapture models for 28 species with habitat as a covariable. For all species, recapture rates between sampling sessions were low and varied from 0.04 for Rainbow Starfrontlets (Coeligena iris) to 0.41 for Stripe‐headed Brushfinches (Arremon assimilis) when averaged across all occupied habitats. Annual survival rates varied from 0.07 for Black‐crested Warblers (Margarornis squamiger) to 0.75 for Violet‐throated Metaltails (Metallura baroni). We found no significant differences in survival rates either among habitats or species grouped by habitat specialization. Because we found similar survival rates in native forest and human‐modified habitats, our results support those of recent studies concerning the potential value of secondary habitats for the conservation of some species of birds in the tropics. However, our conclusions are tempered by the uncertainty around the estimates of survival rates. Despite the relatively long‐term nature of our study, obtaining survival estimates for bird species in this region was challenging, and either more years of study or modification of field protocols may be needed to obtain more precise survival estimates.     

Nitrous oxide emissions from multiple combined applications of fertiliser and cattle slurry to grassland

Identifying forage species that are productive in saline environments is an important research priority in many areas of the world affected by salinity. The salt and waterlogging tolerances of 19 species of Melilotus were evaluated in a series of glasshouse experiments. Measurements taken on each species included: dry matter (DM) production, root growth and development, shoot ion (Na⁺, K⁺ and Cl⁻) concentrations, root porosity, and in vitro estimates of nutritive value. Research on several species was restricted because of their potential as weed risks. Of the remaining species, M. siculus (syn. M. messanensis), an annual species, showed high relative salt and waterlogging tolerances, good DM production under non-stressed and stressed (saline and hypoxic) conditions, a high level of root porosity under stagnant conditions, low tissue ion (Na⁺, Cl⁻) concentrations, and a reasonable dry matter digestibility content (range 66–69%) under highly saline conditions. M. sulcatus ssp. segetalis and M. indicus were also identified as species with good DM production and tolerance to salinity and waterlogging stresses. Further weed risk assessments and field trials on these species are required before they can be promoted for use as pasture forages on saline areas.     

CETACEAN ABUNDANCE IN HAWAIIAN WATERS ESTIMATED FROM A SUMMER/FALL SURVEY IN 2002

Cetacean abundance is estimated for the U.S. Exclusive Economic Zone (EEZ) around the Hawaiian Islands based on a ship line‐transect survey from August to November, 2002. Sighting detection functions are estimated from this and other NOAA research surveys from 1986 to 2002 using a new, multiple‐covariate approach. Twenty‐four species were seen on this survey, including two species (Fraser's dolphin [Lagenodelphis hosei] and sei whale [Balaenoptera borealis]) that had not been previously documented to occur in Hawaiian waters. The most abundant large whales are sperm whales (Physeter macrocephalus) and Bryde's whales (Balaenoptera edeni). The most abundant delphinids are pilot whales (Globicephala macrorhynchus), rough‐toothed dolphins (Steno bredanensis), Fraser's dolphins, spotted dolphins (Stenella attenuata), and striped dolphins (Stenella coeruleoalba). Dwarf and pygmy sperm whales (Kogia sima and Kogia breviceps) and Cuvier's beaked whales (Ziphius cavirostris) are also estimated to be quite abundant. Some of the migratory baleen whales (fin whales [Balaenoptera physalus], sei whales, minke whales [B. acutorostrata], and humpback whales [Megaptera novaeangliae]) were seen only late in the survey. Abundance is estimated for 19 cetacean species. The overall density of cetaceans is low in the study area, especially for delphinids. The precision of density and abundance estimates is generally low for all species because of the low number of sightings.     

Phylogeography of the narrow‐headed vole Lasiopodomys (Stenocranius) gregalis (Cricetidae,Rodentia) inferred from mitochondrial cytochrome b sequences: an echo of Pleistocene prosperity

A species‐wide phylogeographic study of the narrow‐headed vole Lasiopodomys (Stenocranius) gregalis was performed using the mitochondrial (mt) cytochrome b gene. We examined 164 specimens from 50 localities throughout the species distribution range. Phylogeographic pattern clearly demonstrates the division into four major mtDNA lineages with further subdivision. The level of genetic differentiation between them was found to be extremely high even for the species level: about 6–11%. The most striking result of our study is extremely high mutation rate of cytb in L. gregalis. Our estimates suggested its value of 3.1 × 10^?5 that is an order of magnitude higher than previous estimates for Microtus species. The mean estimated time of basal differentiation of the narrow‐headed vole is about 0.8 Mya. This time estimate is congruent with the known paleontological record. The greatest mitochondrial diversity is found in Southern Siberia where all four lineages occur; therewith, three of them are distributed exclusively in that area. The lineage that is distributed in south‐eastern Transbaikalia is the earliest derivate and exhibits the highest genetic divergence from all the others (11%). It is quite probable that with further research, this lineage will turn out to represent a cryptic species. Spatial patterns of genetic variation in populations of the narrow‐headed vole within the largest mt lineage indicate the normal or stepping stone model of dispersal to the north and south‐west from the Altay region in Middle Pleistocene. Both paleontological data and genetic diversity estimates suggest that this species was very successful during most of the Pleistocene, and we propose that climate humidification and wide advance of tree vegetation at the Pleistocene–Holocene boundary promoted range decrease and fragmentation for this typical member of tundra‐steppe faunistic complex. However, we still observe high genetic diversity within isolated fragments of the range.     

Stink bug rostrum length vs. stylet penetration potential

Stink bugs (Hemiptera: Pentatomidae) and related species continue to plague cotton, Gossypium hirsutum L. (Malvaceae), worldwide. Stink bugs utilize their stylets (housed within the rostrum) to feed upon cotton bolls and transmit pathogens that cause seed and boll rot of cotton. Stylet penetration potential of stink bugs is influenced by species and recent observations indicated a phenomenon whereby stink bugs with shorter rostra yielded deeper stylet penetration estimates. The objective of this study was to elucidate the relationship between rostrum length and known stylet penetration estimates for two pairs of similar‐sized pentatomid species: Chinavia hilaris (Say) vs. Euschistus servus (Say), and Oebalus pugnax (Fabricius) vs. Piezodorus guildinii Westwood. For each species, individual rostral segments were measured to yield total lengths, and measurements were compared against known stylet penetration estimates. Chinavia hilaris and P. guildinii have longer rostra than E. servus and O. pugnax, respectively, yet E. servus and O. pugnax yielded deeper stylet penetration estimates. Deeper stylet penetration by species with shorter rostra can be attributed to differences in the lengths of rostral segments 1 and 2. Euschistus servus and O. pugnax each had significantly longer rostral segments 1 and 2 than C. hilaris and P. guildinii, respectively. Also, the cumulative lengths of rostral segments 1 and 2 comprised a higher overall proportion of the entire rostrum length in E. servus and O. pugnax vs. C. hilaris and P. guildinii, respectively. Rostral segments 1 and 2 are instrumental in the feeding mechanics of these phytophagous species; it is clear that their greater length and their role in stylet penetration model calculations – including the lengths of segments 3 and 4 – override the presumption that total rostrum length equates to stylet penetration potential. This novel finding contributes to the general knowledge of stink bug feeding mechanics.     

Life-history,exploitation and extinction risk of the data-poor Baraka's whipray (Maculabatis ambigua) in small-scale tropical fisheries

The Baraka's whipray (Maculabatis ambigua) is a major constituent of small-scale fisheries catch in the south-western Indian Ocean. Despite this, little is known of its life-history or exploitation status. We provide the first estimates of crucial life-history parameters and the maximum intrinsic population growth rate r_max , using specimens collected from small-scale fisheries landings in Kenya, Zanzibar and Madagascar (with northern Madagascar representing a range extension for this species). We assess the relative risk of overexploitation by combining r_max with estimates of total Z , fishing F , and natural M mortality, and an estimate of the exploitation ratio E . The data indicate that Baraka's whipray is a medium-sized, fast-growing, early maturing species, with a relatively long lifespan. This results in a high r_max relative to many other elasmobranchs, which when combined with estimates of F suggests that the species is not at imminent risk of extinction. Yet, estimates of exploitation ratio E indicate likely overfishing for the species, with full recruitment to the fishery being post-maturation and exploitation occurring across a broad range of age and size classes. Thus, Baraka's whipray is unlikely to be biologically sustainable in the face of current fisheries pressures. This paper makes an important contribution to filling the gap in available data and is a step towards developing evidence-based fisheries management for this species. Further, it demonstrates a simple and widely applicable framework for assessment of data-poor elasmobranch exploitation status and extinction risk.     

Estimation of the dispersal of a major pest of maize by cline analysis of a temporary contact zone between two invasive outbreaks

Dispersal is a key factor in invasion and in the persistence and evolution of species. Despite the importance of estimates of dispersal distance, dispersal measurement remains a real methodological challenge. In this study, we characterized dispersal by exploiting a specific case of biological invasion, in which multiple introductions in disconnected areas lead to secondary contact between two differentiated expanding outbreaks. By applying cline theory to this ecological setting, we estimated σ, the standard deviation of the parent–offspring distance distribution, of the western corn rootworm, Diabrotica virgifera virgifera, one of the most destructive pests of maize. This species is currently invading Europe, and the two largest invasive outbreaks, in northern Italy and Central Europe, have recently formed a secondary contact zone in northern Italy. We identified vanishing clines at 12 microsatellite loci throughout the contact zone. By analysing both the rate of change of cline slope and the spatial variation of linkage disequilibrium at these markers, we obtained two σ estimates of about 20 km/generation^1/2. Simulations indicated that these estimates were robust to changes in dispersal kernels and differences in population density between the two outbreaks, despite a systematic weak bias. These estimates are consistent with the results of direct methods for measuring dispersal applied to the same species. We conclude that secondary contact resulting from multiple introductions is very useful for the inference of dispersal parameters and should be more widely used in other species.