Fine-scale spatial genetic structure and gene flow in a small, fragmented population of Sinojackia rehderiana (Styracaceae), an endangered tree species endemic to China

Populations of Sinojackia rehderiana are highly threatened and have small and scattered distribution due to habitat fragmentation and human activities. Understanding changes in genetic diversity, the fine-scale spatial genetic structure (SGS) at different life stages and gene flow of S. rehderiana is critical for developing successful conservation strategies for fragmented populations of this endangered species. In this study, 208 adults, 114 juveniles and 136 seedlings in a 50 × 100-m transect within an old-growth forest were mapped and genotyped using eight microsatellite makers to investigate the genetic diversity and SGS of this species. No significant differences in genetic diversity among different life-history stages were found. However, a significant heterozygote deficiency in adults and seedlings may result from substantial biparental inbreeding. Significant fine-scale spatial structure was found in different life-history stages within 19 m, suggesting that seed dispersal mainly occurred near a mother tree. Both historical and contemporary estimates of gene flow (13.06 and 16.77 m) indicated short-distance gene dispersal in isolated populations of S. rehderiana. The consistent spatial structure revealed in different life stages is most likely the result of limited gene flow. Our results have important implications for conservation of extant populations of S. rehderiana. Measures for promoting pollen flow should be taken for in situ conservation. The presence of a SGS in fragmented populations implies that seeds for ex situ conservation should be collected from trees at least 19-m apart to reduce genetic similarity between neighbouring individuals.     

Distance-limited dispersal promotes coexistence at habitat boundaries: reconsidering the competitive exclusion principle

Understanding the conditions for the stable coexistence of different alleles or species is a central topic in theoretical evolution and ecology. Different causes for stable polymorphism or species coexistence have already been identified but they can be grouped into a limited number of general processes. This article is devoted to the presentation and illustration of a new process, which we call 'habitat boundary polymorphism', and which relies on two key ingredients: habitat heterogeneity and distance-limited dispersal. Under direct competition and with fixed population densities, we show that this process allows for the equilibrium coexistence of more than n types in a n-habitat environment. Distance-limited dispersal indeed creates local maladaptation at habitat edges, which leaves room for the invasion of more generalist alleles or species. This mechanism provides a generic yet neglected process for the maintenance of polymorphism or species coexistence.     

Do edge responses cascade up or down a multi‐trophic food web?

Despite nearly 100?years of edge studies, there has been little effort to document how edge responses 'cascade' to impact multi-trophic food webs. We examined changes within two, four-tiered food webs located on opposite sides of a habitat edge. Based on a 'bottom-up' resource-based model, we predicted plant resources would decline near edges, causing similar declines in specialist herbivores and their associated predators, while a generalist predator was predicted to increase due to complementary resource use. As predicted, we found declines in both specialist herbivores and predators near edges, but, contrary to expectations, this was not driven by gradients in plant resources. Instead, the increase in generalist predators near edges offers one alternative explanation for the observed declines. Furthermore, our results suggest how recent advances in food web theory could improve resource-based edge models, and vice versa.     

Parallel declines in species and genetic diversity in tropical forest fragments

The potential for parallel impacts of habitat change on multiple biodiversity levels has important conservation implications. We report on the first empirical test of the 'species-genetic diversity correlation' across co-distributed taxa with contrasting ecological traits in the context of habitat fragmentation. In a rainforest landscape undergoing conversion to oil palm, we show that depauperate species richness in fragments is mirrored by concomitant declines in population genetic diversity in the taxon predicted to be most susceptible to fragmentation. This association, not seen in the other species, relates to fragment area rather than isolation. While highlighting the over-simplification of extrapolating across taxa, we show that fragmentation presents a double jeopardy for some species. For these, conserving genetic diversity at levels of pristine forest could require sites 15-fold larger than those needed to safeguard species numbers. Importantly, however, each fragment contributes to regional species richness, with larger ones tending to contain more species.     

Activation of protein kinase C suppresses fragmentation of pig oocytes aged in vitro

When cultured for an extended time, pig oocytes that matured in vitro to the stage of metaphase II undergo the complex process designated as ageing. Under our conditions, some pig oocytes aged 3 days remained at the stage of metaphase II (22%), but others underwent spontaneous parthenogenetic activation (45%), and still others perished through fragmentation (28%) or lysis (5%). Activation of protein kinases C (PKCs) using phorbol-12-myristate-13-acetate (PMA) protects oocytes from fragmentation. None of the oocytes were fragmented after 3 days of aging in 50 nM of PMA. A similar effect (8% of fragmented oocytes) was observed after a 3-day treatment of aging oocytes with 100 μM of 1-stearoyl-2arachidonoyl-sn-glycerol (STEAR). PMA and STEAR activate both calcium-dependent and calcium-independent PKCs. This combined effect on PKCs seems to be essential for the protection of oocytes from fragmentation. Neither the specific activator of calcium-dependent PKCs 1-oleoyl-2-acetyl-sn-glycerol (OLE) nor the specific activator of calcium-independent PKCs dipalmitoyl-l-α-phosphatidylinositol-3,4,5-triphosphate heptaammonium salt (DIPALM) suppressed the fragmentation of aging pig oocytes. Twenty-one percentage of oocytes fragmented when aged for 3 days in 10 μM OLE and 26% of aged oocytes fragmented in 100 nM of DIPALM. However, fragmentation was significantly suppressed to 7% when the oocytes were exposed to the combination of both 10 μM OLE and 100 nM DIPALM. Aging pig oocytes cultured for 1 day with PMA maintained a high capability of being parthenogenetically activated (86% of activated oocytes), using calcium ionophore with 6-dimethylaminopurine. Ageing oocytes treated with PMA also had high capability of cleavage (82%) after their artificial parthenogenetic activation. However, their ability to develop to the stage of blastocyst (12%) was suppressed when compared with oocytes activated immediately after their maturation (29%).     

Changes in the soluble bone proteome of reared white seabream (Diplodus sargus) with skeletal deformities

One of the main constrains for commercial aquaculture production of white seabream (Diplodus sargus) is the high incidence of skeletal malformations in reared fish. The purpose of this study was to obtain a better understanding of the mechanisms involved in the development of these types of skeletal malformations by comparative proteomic analysis of the vertebral column of normal and deformed fish using 2DE for protein separation and MS for protein identification. We observed a 3.2 and 3.4-fold increase in the expression of two tropomyosin isoforms, one of which (tropomyosin-4) is essential for the motility and polarization cycles of osteoclasts. Furthermore, a 1.6, 1.7 and 1.8-fold increase in three parvalbumin spots was detected, suggesting a cellular response to increased intracellular Ca²⁺ levels. These results can be interpreted as signs of increased cellular activity in the bone of white seabream with skeletal deformities coupled to a higher degree of calcium mobilization, which elicits further studies into the use of these proteins as indicators of skeletal metabolic state.     

Predation of experimental nests is linked to local population dynamics in a fragmented bird population

Artificial nest experiments (ANEs) are widely used to obtain proxies of natural nest predation for testing a variety of hypotheses, from those dealing with variation in life-history strategies to those assessing the effects of habitat fragmentation on the persistence of bird populations. However, their applicability to real-world scenarios has been criticized owing to the many potential biases in comparing predation rates of artificial and natural nests. Here, we aimed to test the validity of estimates of ANEs using a novel approach. We related predation rates on artificial nests to population viability analyses in a songbird metapopulation as a way of predicting the real impact of predation events on the local populations studied. Predation intensity on artificial nests was negatively related to the species' annual population growth rate in small local populations, whereas the viability of large local populations did not seem to be influenced, even by high nest predation rates. The potential of extrapolation from ANEs to real-world scenarios is discussed, as these results suggest that artificial nest predation estimates may predict demographic processes in small structured populations.     

Higher climate warming sensitivity of Siberian larch in small than large forest islands in the fragmented Mongolian forest steppe

Forest fragmentation has been found to affect biodiversity and ecosystem functioning in multiple ways. We asked whether forest size and isolation in fragmented woodlands influences the climate warming sensitivity of tree growth in the southern boreal forest of the Mongolian Larix sibirica forest steppe, a naturally fragmented woodland embedded in grassland, which is highly affected by warming, drought, and increasing anthropogenic forest destruction in recent time. We examined the influence of stand size and stand isolation on the growth performance of larch in forests of four different size classes located in a woodland‐dominated forest‐steppe area and small forest patches in a grassland‐dominated area. We found increasing climate sensitivity and decreasing first‐order autocorrelation of annual stemwood increment with decreasing stand size. Stemwood increment increased with previous year's June and August precipitation in the three smallest forest size classes, but not in the largest forests. In the grassland‐dominated area, the tree growth dependence on summer rainfall was highest. Missing ring frequency has strongly increased since the 1970s in small, but not in large forests. In the grassland‐dominated area, the increase was much greater than in the forest‐dominated landscape. Forest regeneration decreased with decreasing stand size and was scarce or absent in the smallest forests. Our results suggest that the larch trees in small and isolated forest patches are far more susceptible to climate warming than in large continuous forests pointing to a grim future for the forests in this strongly warming region of the boreal forest that is also under high land use pressure.     

Habitat selection by capercaillie in summer and autumn: Is bilberry important?

The use of habitat by female and male adult capercaillie Tetrao urogallus during summer and autumn was studied by comparing the distribution of radio locations of birds with the availability of habitat at forest stand, home range and landscape level in an area of the Bavarian Alps, Germany. Capercaillie preferred forests with structural features typical of their main distribution range, the boreal forest: they selected large patches of old forest with moderate canopy cover of about 50%, and a well developed field layer with high proportions of bilberry Vaccinium myrtillus. Hens selected both home ranges and sites within home ranges in old forest. Ranges selected by cocks did not differ from availability in the study area, but they preferred old forest within their ranges. The size of home ranges was negatively related to bilberry cover both in hens and cocks. The distribution of bilberry also determined habitat use by capercaillie at the landscape scale. The study demonstrated that bilberry is the major determinant of the selection of habitat by capercaillie in landscapes with sparse and fragmentary cover of ericaceous shrubs, such as central Europe.