OPTIMAL REPRODUCTIVE EFFORT IN STOCHASTIC,DENSITY-DEPENDENT ENVIRONMENTS

The amount of effort organisms should put into reproducing at any given time has been a matter of debate for many years. Early models suggested a simple rule of thumb: iteroparity should be favored when juvenile survival is relatively variable and semelparity when adult survival is relatively variable. When more mathematically complex models were developed, these simple conclusions were found to be special cases. Variability can select toward iteroparity or semelparity depending on a number of factors irrespective of relative adult/juvenile survival (e.g, the density-independent models of Orzack and Tuljapurkar). Using new techniques, we estimate the ESS reproductive effort for stage-structured models in density-dependent and stochastic conditions. We find that variability causes significant changes in reproductive effort, these changes are often small (± 10% of determinstic ESS effort, but up to 50% change in some instances), and the amount that effort increases or decreases depends on many factors (e.g., the deterministic population dynamics, the vital rates affected by density, the amount of variation, the correlations between the vital rates, the distribution from which the variation is drawn, and the deterministic ESS effort). In a variable environment, semelparity is the ESS in only 3.5% of cases; iteroparity is the rule.     

Plant species richness in continental southern Siberia: effects of pH and climate in the context of the species pool hypothesis

Aim Many high‐latitude floras contain more calcicole than calcifuge vascular plant species. The species pool hypothesis explains this pattern through an historical abundance of high‐pH soils in the Pleistocene and an associated opportunity for the evolutionary accumulation of calcicoles. To obtain insights into the history of calcicole/calcifuge patterns, we studied species richness–pH–climate relationships across a climatic gradient, which included cool and dry landscapes resembling the Pleistocene environments of northern Eurasia. Location Western Sayan Mountains, southern Siberia. Methods Vegetation and environmental variables were sampled at steppe, forest and tundra sites varying in climate and soil pH, which ranged from 3.7 to 8.6. Species richness was related to pH and other variables using linear models and regression trees. Results Species richness is higher in areas with warmer winters and at medium altitudes that are warmer than the mountains and wetter than the lowlands. In treeless vegetation, the species richness–pH relationship is unimodal. In tundra vegetation, which occurs on low‐pH soils, richness increases with pH, but it decreases in steppes, which have high‐pH soils. In forests, where soils are more acidic than in the open landscape, the species richness–pH relationship is monotonic positive. Most species occur on soils with a pH of 6–7. Main conclusions Soil pH in continental southern Siberia is strongly negatively correlated with precipitation, and species richness is determined by the opposite effects of these two variables. Species richness increases with pH until the soil is very dry. In dry soils, pH is high but species richness decreases due to drought stress. Thus, the species richness–pH relationship is unimodal in treeless vegetation. Trees do not grow on the driest soils, which results in a positive species richness–pH relationship in forests. If modern species richness resulted mainly from the species pool effects, it would suggest that historically common habitats had moderate precipitation and slightly acidic to neutral soils.     

Relationship of inbreeding with sperm quality and reproductive success in Mexican gray wolves

The ultimate goal of the Mexican gray wolf Canis lupus baileyi captive management program is reintroduction of healthy individuals into wild habitats. To this end, zoo population managers work to provide not only for the physical well-being but also for the genetic health of these animals. However, the very limited genetic founder base, exacerbated by breeding within three distinct lineages, resulted in very high coefficients of inbreeding. Because support for measurable levels of inbreeding depression in the captive wolf population, as defined by reductions in common fitness measures such as juvenile survival or reproductive success, has been weak, we investigated the potential effects on male reproductive capacity. We analyzed semen samples from wolves from all three lineages and compared them with samples from subsequent lineage crosses and from generic gray wolves. We not only found a significant effect of inbreeding on sperm quality but we related both inbreeding and sperm quality to reproductive success. Samples from male offspring of lineage crosses, with inbreeding coefficients of zero were similar in quality to those from generic gray wolves. However, samples from a limited number of offspring from back-crosses were of extremely poor quality. Although it is reassuring that sperm quality was so much improved in male offspring of lineage crosses, the concomitant reduction in inbreeding coefficient does not eliminate the potentially deleterious alleles. Our results demonstrate that sperm quality is an important indicator of fertility and reproductive success in Mexican wolves. In addition, our data lend further support to the presence of inbreeding depression in this taxon.     

Variation in food availability mediate the impact of density on cannibalism,growth, and survival in larval yellow spotted mountain newts (Neurergus microspilotus): Implications for captive breeding programs

In this study, we examined cannibalistic behavior, growth, metamorphosis, and survival in larval and post‐metamorph endangered yellow spotted mountain newts Neurergus microspilotus hatched and reared in a captive breeding facility. We designed a 2 × 2 factorial experiment, crossing two levels of food with two levels of density including high food/high density, high food/low density, low food/high density, and low food/low density. The level of cannibalistic behavior (including the loss of fore and hind limbs, missing toes, tail, gills, body damage, and whole body consumption) changed as the larvae grew, from a low level during the first 4 weeks, peaking from weeks 7 to 12, and then dropped during weeks 14–52. Both food level and density had a significant effect on cannibalism. The highest frequency of cannibalism was recorded for larvae reared in the low food/high density and lowest in high food/low density treatments. Growth, percent of larval metamorphosed, and survival were all highest in the high food/low density and lowest in low food/high density treatment. Food level had a significant effect on growth, metamorphosis, and survival. However, the two levels of density did not influence growth and metamorphosis but showed a significant effect on survival. Similarly, combined effects of food level and density showed significant effects on growth, metamorphosis, and survival over time. Information obtained from current experiment could improve productivity of captive breeding facilities to ensure the release of adequate numbers of individuals for reintroduction programs. Zoo Biol. 35:513–521, 2016. © 2016 The Authors. Zoo Biology published by Wiley Periodicals, Inc.     

Environmental constraints and call evolution in torrent‐dwelling frogs

Although acoustic signals are important for communication in many taxa, signal propagation is affected by environmental properties. Strong environmental constraints should drive call evolution, favoring signals with greater transmission distance and content integrity in a given calling habitat. Yet, few empirical studies have verified this prediction, possibly due to a shortcoming in habitat characterization, which is often too broad. Here we assess the potential impact of environmental constraints on the evolution of advertisement call in four groups of torrent‐dwelling frogs in the family Ranidae. We reconstruct the evolution of calling site preferences, both broadly categorized and at a finer scale, onto a phylogenetic tree for 148 species with five markers (～3600 bp). We test models of evolution for six call traits for 79 species with regard to the reconstructed history of calling site preferences and estimate their ancestral states. We find that in spite of existing morphological constraints, vocalizations of torrent‐dwelling species are most probably constrained by the acoustic specificities of torrent habitats and particularly their high level of ambient noise. We also show that a fine‐scale characterization of calling sites allows a better perception of the impact of environmental constraints on call evolution.     

Survival rates of captive‐bred Asian Houbara Chlamydotis macqueenii in a hunted migratory population

Asian Houbara Chlamydotis macqueenii numbers are declining as a result of unsustainable levels of hunting and poaching, with the main conservation response being population reinforcement through the release of captive‐bred birds. We assessed the contribution of captive breeding to the species’ conservation by examining the fates of 65 captive‐bred birds fitted with satellite transmitters and released during spring (March–May) and autumn (August) into breeding habitat in Uzbekistan. Of the released birds, 58.5% survived to October, the month favoured by Emirati hunters in Uzbekistan, but only 10.8% of those released survived the winter to return as subadults next spring. To mitigate and compensate for the loss of wild adults to hunting, the number of released birds needs to be an order of magnitude higher than hunting quotas (with a release of between 1640 and 1920 required for a hypothetical quota of 200), indicating that releases may be costly and do not remove the need for a biologically determined sustainable hunting quota.     

Fossil wood charcoal assemblages from Elands Bay Cave, South Africa: implications for Late Quaternary vegetation and climates in the winter-rainfall fynbos biome

Aim The aim of this paper is to analyse fossil charcoal deposits, largely identified to the species level and spanning a sequence from the late Holocene to < 40,000 BP , in order to reconstruct Late Quaternary vegetation and climatic patterns in the western (winter-rainfall) fynbos biome of South Africa. Location The charcoals were excavated from the Elands Bay Cave (32°19S, 18°20E) on the semiarid (200–250 mmyr^?1), winter-rainfall coastline of the western fynbos biome. Methods Patterns in the charcoal data set over time were sought by manual sorting of the charcoal×sample matrix, as well as by subjecting the data to multivariate analysis. Palaeoclimatic reconstruction was attempted by comparing the climatic controls on contemporary vegetation communities that resembled the fossil assemblages. Charcoal diversity was modelled using sample age and number of charcoal fragments as explanatory variables. Results The fossil assemblages ranged from xeric communities (similar to those presently occurring at the site) during the Holocene, to more mesic thicket and fynbos vegetation in the terminal Pleistocene, to Afromontane forest and riverine woodland communities after about 18,000 BP . Diversity of the charcoal samples increased monotonically with increasing sample age. Main conclusions The results suggest that, unlike the eastern fynbos biome, which is under fundamentally different climatic controls, soil moisture conditions in the western part of the biome were higher in the Last Glacial than during the Holocene. This scenario may help to explain the higher regional richness and associated diversification in the western than eastern part of the biome.     

INTRACELLULAR DIMETHYLSULFOXIDE (DMSO) IN UNICELLULAR MARINE ALGAE: SPECULATIONS ON ITS ORIGIN AND POSSIBLE BIOLOGICAL ROLE

Recent studies have established that aqueous phase concentrations of dimethylsulfoxide (DMSO) often exceed those of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS). Yet, in comparison to DMSP and DMS, DMSO remains a poorly understood component of the marine sulfur cycle. Much of what is known about the mechanisms for the formation and loss for DMSO is inferred from laboratory experiments, and no explanation exists to rationalize how a large pool of DMSO is maintained. One formation pathway that, until very recently, has been ignored involves the direct synthesis of DMSO by marine phytoplankton. This review examines some of the circumstantial evidence for DMSO in marine particulate material and recent reports containing preliminary data for particulate DMSO (DMSO_p) in the marine environment. Drawing on literature from a range of scientific disciplines, speculations on the possible origins and biological functions of intracellular DMSO are also made. On the basis of its physicochemical properties, intracellular DMSO could have a potential role as a cryoprotectant, a specialist cryo-osmoregulator in extreme environments, an intracellular electrolyte modifier, and a free-radical scavenger. The review also assesses the impact of DMSO_p at both the organism and the global level. Consideration is given to the marine biogeochemical cycling of sulfur and potential links to climate control.