Alternative Habitats Research Articles

Old rural parks support higher biodiversity than forest remnants

One of the main challenges in biodiversity conservation is to curb a further degradation and loss of high-quality habitats. In agricultural matrix landscapes, the detection of alternative habitats for habitat specialists may be a solution. Historic old parks or landscape gardens around manor houses and castles are cultural heritage of nobles, but their value in harbouring biodiversity is poorly acknowledged. Therefore we evaluated the potential of old rural parks to serve as a habitat for nemoral forest species. We recorded stand structure and the presence of forest biodiversity indicators in 74 closed-canopy stands of historic parks and compared them with 93 neighbouring mature forest remnants on ancient forest land. We estimated the importance of stand structure in relation to habitat type on biodiversity indicators. Finally we suggest single-value indicator-complexes for the cost-efficient assessment of the conservation value of forests and forest-like habitats. Park stands outclassed reference forests in several individual structural characteristics, and in combined indicators of habitat quality and biodiversity. Forests had higher estimates for the combined indicator of dead wood, but large-diameter dead wood types were more abundant in parks. Woodpeckers, several old-growth indicator epiphytes and forest herbs had successfully become established in planted forest-like park fragments. Old rural parks resemble high-conservation-value forests more than the best preserved contemporary forest remnants. After the century needed to overcome immigration delay, old parks do provide a refugium for temperate deciduous forest species. Consequently, biodiversity-targeted management should retain and enhance old-growth attributes in forests and on the peripheries of parks: e.g. preserving old trees to provide service for epiphytes, hollow trees and an understorey mosaic for birds and bats; dead wood elements for saproxylic insects and fungi; limited mowing frequency and increased cutting height for forest herbs. Forestry should enhance the recovery of mixed deciduous stands and avoid conifer plantations.

Sporopachydermia cereana fungaemia in refractory leukaemia presenting as breakthrough infection during micafungin therapy

The Sporopachydermia cereana species lives in decaying stems of cactus and is exceptionally rare as a human pathogen. A 57-year-old man with therapy-refractory acute promyelocytic leukaemia developed severe neutropaenia. After about 3 weeks of micafungin used as prophylaxis, he developed high fever, multiple pulmonary nodular infiltrates and a painful leg lesion. Blood culture yielded a yeast which was not identified by the Vitek 2 system. On ITS1-5.8S-ITS2 gene sequencing, the isolate was identified as S. cereana. Antifungal sensitivity by the Etest showed that the minimum inhibitory concentration for fluconazole was 0.75 μg/mL, and for anidulafungin, it was >32 μg/mL. He responded to liposomal amphotericin B but later died of Escherichia coli septicaemia. There were no cactus plants in the vicinity, suggesting that S. cereana might have alternative habitats.

Conflict of human–wildlife coexistence

Carter et al. (1) used data on spatial overlap of tigers and people to conclude that human–tiger coexistence is possible at fine spatial scales. The question then is whether spatial overlap suggests that human–tiger coexistence is in fact a viable strategy for their mutual well-being in the long run. Coexistence, or rather its absence between large carnivores and humans, is an oft-repeated theme in conservation biology. The results presented by Carter et al. (1) support this recognition; tigers were detected less frequently near human populations and the probability of their detection increased with distance from human settlement. Although this finding is indicative of a scenario where tigers are being pushed into areas of low human activity, the authors argue that it is a mechanism by which tigers coexist with people. We contend that the same result could just as easily be interpreted as increasing anthropogenic pressures hemming in a tiger population that is deprived of alternative habitats.

논습지에 도래하는 수조류의 서식지 이용과 개체군 특성

BACKGROUND: As natural wetlands are decreased by increment of human demand, the importance of rice fields as an alternative habitat for waterbirds is well documented. However, the relationship between waterbirds use and management practice of rice fields has not been fully understood. The present study attempted to understand the changes in temporal abundance of waterbirds and their preference for habitat types in rice fields all year round. METHODS AND RESULTS: Waterbirds census were conducted in rice fields around Asan bay in Korea during April 2009-March 2010 and April 2011-March 2012. In the bird counts, the locations of the observed birds on a 1/2,500 map were recorded along with the local habitat type (paddy, ditch, levee, road). Thirty five species of waterbirds recorded in the rice fields during the survey period and three major groups (shorebirds, herons, and waterfowls) were characterized according to season and micro-habitat use. Shorebirds visited a flooded paddy for feeding during their spring migration season (April-May), and herons used the rice field as feeding sites during their breeding periods (April-October). Most waterfowls were observed in a dry paddy to feed a fallen rice seed and stubs during the winter season (September-March). Waterbird groups selectively used micro-habitats in rice field. Shorebirds and waterfowls mainly preferred at rice paddies, while herons were attracted to most habitat types. CONCLUSION(S): Rice fields supported various waterbirds all year round and waterbird communities using the rice fields were dramatically changed according to seasonal change of rice field condition.

Host selection and parasitism behavior of Lysiphlebus testaceipes: Role of plant, aphid species and instar

The aphid parasitoid Lysiphlebus testaceipes is a potentially valuable biological control agent of Aphis gossypii a major worldwide pest of cotton. One means of increasing the abundance of a biological control agent is to provide an alternative host habitat adjacent to cropping, from which they can provide pest control services in the crop. Host selection and parasitism rate of an alternative host aphid, Aphis craccivora by L. testaceipes were studied in a series of experiments that tested its host suitability relative to A. gossypii on cotton, hibiscus and mungbean. Host acceptance, as measured by number of ovipositions was much greater in A. craccivora compared to A. gossypii, while more host aphids were accepted on mungbean than cotton. When given a choice L. testaceipes attacks more 4th instar and adult stages (63% and 70%, respectively) of both hosts than 2nd instar nymphs (47%). In a switching (host choice) experiment, L. testaceipes preferentially attacked A. craccivora on mungbean over A. gossypii on cotton. Observations of parasitoid contact with A. gossypii cornicle secretion suggest it provides a useful deterrent against parasitoid attack. From these experiments it appears L. testaceipes has a preference for A. craccivora and mungbean compared to A. gossypii and cotton, in this respect using A. craccivora and mungbean as alternative habitat may not work as the parasitoid is unlikely to switch away from its preferred host.

Climate, Management and Habitat Associations of Avian Fauna in Restored Wetlands of California’s Central Valley, USA

The Wetlands Reserve Program (WRP) is one of several programs implemented by the United States Department of Agriculture to facilitate natural resource management on private lands. Since the WRP’s inception approximately 29,000 ha in California’s Central Valley (CCV) have been restored. However until now, actual benefits of the program to wildlife have never been evaluated. Hydrology in the CCV has been heavily modified and WRP wetlands are managed primarily to support wintering waterfowl. We surveyed over 60 WRP easements in 2008 and 2009 to quantify avian use and categorized bird species into 11 foraging guilds. We detected over 200 bird species in 2008 and 119 species in 2009, which is similar to or higher than numbers observed on other managed sites in the same area. We found that actively managed WRP wetlands support more waterfowl than sites under low or intermediate management, which is consistent with intended goals. Despite reported water shortages, greater upland and un-restored acreage in the southern CCV, WRP wetlands support large numbers of waterfowl and shorebirds, particularly in the early fall months. This is probably due to the severe lack of alternative habitat such as wildlife friendly crops at appropriate stages of the migration cycle. Improved access to water resources for hydrological management would greatly enhance waterfowl use in the southern CCV.

Natural or Artificial? Habitat-Use by the Bull Shark, Carcharhinus leucas

BackgroundDespite accelerated global population declines due to targeted and illegal fishing pressure for many top-level shark species, the impacts of coastal habitat modification have been largely overlooked. We present the first direct comparison of the use of natural versus artificial habitats for the bull shark, Carcharhinus leucas, an IUCN ‘Near-threatened’ species - one of the few truly euryhaline sharks that utilises natural rivers and estuaries as nursery grounds before migrating offshore as adults. Understanding the value of alternate artificial coastal habitats to the lifecycle of the bull shark is crucial for determining the impact of coastal development on this threatened but potentially dangerous species.Methodology/FindingsWe used longline surveys and long-term passive acoustic tracking of neonate and juvenile bull sharks to determine the ontogenetic value of natural and artificial habitats to bull sharks associated with the Nerang River and adjoining canals on the Gold Coast, Australia. Long-term movements of tagged sharks suggested a preference for the natural river over artificial habitat (canals). Neonates and juveniles spent the majority of their time in the upper tidal reaches of the Nerang River and undertook excursions into adjoining canals. Larger bull sharks ranged further and frequented the canals closer to the river mouth.Conclusions/SignificanceOur work suggests with increased destruction of natural habitats, artificial coastal habitat may become increasingly important to large juvenile bull sharks with associated risk of attack on humans. In this system, neonate and juvenile bull sharks utilised the natural and artificial habitats, but the latter was not the preferred habitat of neonates. The upper reaches of tidal rivers, often under significant modification pressure, serve as nursery sites for neonates. Analogous studies are needed in similar systems elsewhere to assess the spatial and temporal generality of this research.

Evaluation of secondary forests as alternative habitats to primary forests for flower-visiting insects

Although primary forests are important for biological conservation, the value of secondary forests for forest-dependent organisms needs to be evaluated when habitat restoration is required. We examined whether flower-visiting insects can use secondary forests as alternative habitats to primary forests. In particular, we compared assemblages of bees (Anthophila) and flower longhorn beetles (Lepturinae: Cerambycidae) in young secondary, mature secondary, and primary forests. Our results showed that more bee species were captured in primary and mature secondary forests than in young secondary forests, and flower longhorn beetle species were captured more frequently in primary forests than in mature and young secondary forests. Ordination showed that the communities in the three forest types were not statistically identical, which indicated that secondary forests cannot provide an absolute alternative habitat to primary forests for bees and flower longhorn beetles. However, the results also suggest that as secondary forests mature, more primary forest species would be able to use secondary forests as habitats. This implies that restoration from other land uses, such as monoculture plantations, to secondary forests could help to promote the faunal biodiversity of primary forests.

Microsatellite length variation in candidate genes correlates with habitat in the gilthead sea bream Sparus aurata

The genetic basis and evolutionary implications of local adaptation in high gene flow marine organisms are still poorly understood. In several Mediterranean fish species, alternative migration patterns exist between individuals entering coastal lagoons that offer favourable conditions for growth and those staying in the sea where environmental conditions are less subject to rapid and stressful change. Whether these coexisting strategies are phenotypically plastic or include a role for local adaptation through differential survival needs to be determined. Here, we explore the genetic basis of alternate habitat use in western Mediterranean populations of the gilthead sea bream (Sparus aurata). Samples from lagoonal and open-sea habitats were typed for three candidate gene microsatellite loci, seven anonymous microsatellites and 44 amplified fragment length polymorphism markers to test for genotype-environment associations. While anonymous markers globally indicated high levels of gene flow across geographic locations and habitats, non-neutral differentiation patterns correlated with habitat type were found at two candidate microsatellite loci located in the promoter region of the growth hormone and prolactin genes. Further analysis of these two genes revealed that a mechanism based on habitat choice alone could not explain the distribution of genotype frequencies at a regional scale, thus implying a role for differential survival between habitats. We also found an association between allele size and habitat type, which, in the light of previous studies, suggests that polymorphisms in the proximal promoter region could influence gene expression by modulating transcription factor binding, thus providing a potential explanatory link between genotype and growth phenotype in nature.

Tunisian man‐made wetlands as alternative habitats for waterbirds and their role for conservation

AbstractThe distribution of wintering waterbirds within some Tunisian artificial wetlands (AW) was studied during the 2004–2007 stable wintering periods. The survey has regarded 88 wetlands including 27 large dams, 25 hill dams and 36 hill lakes. We identified 42,840 individuals representing seven orders, eleven families, 37 species and six functional groups: dabbling ducks, grazing waterfowl, fish‐eaters, deep‐water foragers, shoreline foragers and waders. The population structure analysis showed an absolute dominance of the deep‐water foragers with approximately 82% of observed waterbirds. The total abundance survey showed a fluctuation of population sizes and richness, from thousands to few individuals and from 1 to 25 species, respectively. Analysis results showed that the species distribution is governed by several ecological factors and there was a significant correlation between species abundance and richness and some habitat variables such as area, depth, age, plant cover and hunting disturbance. Investigated AW revealed a significant carrying capacity and refuge serving for the conservation of numerous wintering and endangered waterbird species of high nature conservation value, the White‐headed Duck Oxyura leucocephala that has been observed with relatively high numbers representing more than 40% of the assessed Tunisian–Algerian population.

The importance of the surroundings: are bird communities of riparian galleries influenced by agroforestry matrices in SW Iberian Peninsula?

The remaining riparian stretches are often the unique suitable habitats for forest breeding birds in Mediterranean landscapes undergoing long-term changes. Understanding the interactions between riparian zones and their surroundings is critical to establish successful management actions. We assessed the influence of surrounding matrix on riparian bird communities and the use of riparian galleries as surrogate habitats for the forest passerine communities of southwestern Iberia. We used point counts in three simultaneous sampling stations, one in the riparian gallery and two in the adjacent matrix. Three matrix types were selected with a decreasing tree density gradient: dense montado, sparse montado, and open agricultural areas. Data were analysed with redundancy analysis and differences in species’ occurrences were tested with one-way ANOVA. In riparian galleries, we found bird species belong to three ecological guilds: riparian, woodland, and edge guilds. The richness of bird guilds and the occurrence of some species depended on the surrounding matrix type. Riparian bird richness was constant in all surrounding matrices, woodland bird guild was richer in galleries embedded in dense montados, and edge guild in riparian galleries surrounded by sparse montados. Five among 19 assessed species were influenced by matrix type, within particular a few strictly riparian species. Species richness increased close to riparian galleries, due to the increase in habitat heterogeneity and resource availability for birds in densely vegetated riversides. However, the occurrence of some bird species differed according to the type of surrounding matrix. The matrix type explained most of the variance in riparian bird assemblages. Some woodland birds have used riparian galleries as surrogate habitat. Our study suggests that land use in the surrounding matrices must be taking into account for the management and rehabilitation of watercourses and bird conservation actions.

Limitations of habitats as biodiversity surrogates for conservation planning in estuaries

Increasing pressures on global biodiversity and lack of data on the number and abundance of species have motivated conservation planners and researchers to use more readily available information as proxies or surrogates for biodiversity. "Habitat" is one of the most frequently used surrogates but its assumed value in marine conservation planning is not often tested. The present study developed and tested three alternative habitat classification schemes of increasing complexity for a large estuary in south-east Australia and tested their effectiveness in predicting spatial variation in macroinvertebrate biodiversity and selecting estuarine protected areas to represent species. The three habitat classification schemes were: (1) broad-scale habitats (e.g., mangroves and seagrass), (2) subdivision of each broad-scale habitat by a suite of environmental variables that varied significantly throughout the estuary, and (3) subdivision of each broad-scale habitat by the subset of environmental variables that best explained spatial variation in macroinvertebrate biodiversity. Macroinvertebrate assemblages differed significantly among the habitats in each classification scheme. For each classification scheme, habitat richness was significantly correlated with species richness, total density of macroinvertebrates, assemblage dissimilarity, and summed irreplaceability. However, in a reserve selection process designed to represent examples of each habitat, no habitat classification scheme represented species significantly better than a random selection of sites. Habitat classification schemes may represent variation in estuarine biodiversity; however, the results of this study suggest they are inefficient in designing representative networks of estuarine protected areas.

Characterization of sediment contamination patterns by hydrophobic pesticides to preserve ecosystem functions of drainage lakes

Many drainage basins are terminal recipients of hydrophobic contaminants such as pesticides. To minimize adverse effects of the contaminated sediments on wildlife, it is important to understand sediment contamination patterns. This study was conducted at the Salton Sea, which is a heavily polluted large lake in southern California, USA, with the purpose to identify areas with minimal contamination so as to support species conservation. We investigated the horizontal and vertical distribution of 14 organochlorine pesticides (OCPs) and 12 currently used pesticides (CUPs) in playas at locations near the drainage outfalls. The data were subjected to spatial analysis using Kriging interpolation and converted to contour maps. Statistical comparisons were made among different areas, between different sediment depths, and between air-exposed and submerged sediments. Various OCPs were found near two drainage inlets, with mean concentrations of 6–30 μg kg−1 in air-exposed sediments and 3–18 μg kg−1 in submerged sediments. Chlordane (detected frequency, DF = 77 %) and DDT derivatives (DF = 100 %) were among the most frequently detected OCP. Significantly higher concentrations were found in air-exposed sediments than in submerged sediments, and in subsurface sediments than in surface sediments (P < 0.01), suggesting historical deposition and burial. Sediments at many locations exceeded the threshold levels for DDE. A total of seven CUPs were detected with the maximum ∑CUPs concentration of up to 27 μg kg−1. Bifenthrin was the dominant CUP contaminant, representing more than 60 % of ∑CUPs for most samples with the highest concentration of 26 μg kg−1. Findings from this study provide a snapshot of the spatial distribution in both horizontal and vertical directions of hydrophobic pesticides in a drainage-dominated lake, and such information and the method of investigation may be used for identifying areas of minimal contamination as alternative habitats for this and other impacted lakes.

Association of brook trout andOncorhynchusspp. with large wood jams in a Lake Superior tributary in a northern old‐growth watershed

AbstractWood in streams functions as fish habitat, but relationships between fish abundance (or size) and large wood in streams are not consistent. One possible reason for variable relationships between fish and wood in streams is that the association of fish with wood habitat may depend on ecological context such as large‐scale geomorphology. We studied the relationship between salmonid assemblages and large wood jams (LWJ) in four settings that differed geomorphically at the scale of the stream corridor along a tributary toLakeSuperior in old‐growth conifer–hardwood forest in northernMichigan. The focal fish species of this study were brook trout (Salvelinus fontinalis), which were wild in the stream. Relocation efforts for coaster brook trout (an adfluvial life history variant of brook trout) were ongoing in the study stream. We measured fish abundance and length in pairs of pools of similar size and substrate, but varying in the presence ofLWJ; this allowed us to evaluate associations of fish simply with the presence ofLWJrather than with other channel or flow‐shaping functions ofLWJ. The length ofOncorhynchusspp. and young introduced brook trout was not strongly correlated withLWJpresence; however, the presence ofLWJin pools was positively correlated with larger wild brook trout. We also found that the correspondence ofLWJwith the abundance of salmonids appears to be moderated by the presence of alternative habitat in this relatively natural, old‐growth forest stream.

KAJIAN KOMPOSISI SERANGGA POLINATOR PADA TUMBUHAN PENUTUP TANAH DI PONCOKUSUMO – MALANG:

The use of pesticides on agricultural land has a negative impact on health, economic, and environment. The using of variety of ground cover plants as refugia area are expected to be an alternative habitat for pollinators insect in plants: Cyperus rotundus L., Bidens pilosa L., Commelina difussa L., Capsicum frutescens L., and Ageratum conyzoides L. Observations made by visual control. This reseacch aims to know the composition of pollinators insect visit of ground cover plants and analyze their patterns. Analysis of the data structure of insect communities in the spring and the fruit season obtained from INP and diversity (Shannon-Winner Index). Parameters are compared to diversity and abundance with ANOVA test, composition using Morisita Index. The results show that the abundance of insect pollinators of spring higher at 7 families (31%) with H '= 1.698 instead of the fruit season is 6 families (25%) with H' = 1.600. Abundance and diversity of pollinators insect in the spring and fruit season with a significance of P < 0.05. Morisita similarity index of 82%. Analysis of environmental factors of temperature, humidity, and light intensity on the abundance of insect pollinators found positive correlation with R-square 87.5%.

Kajian komposisi serangga polinator pada tumbuhan penutup tanah di Poncokusumo-Malang

The use of pesticides on agricultural land has a negative impact on health, economic, and environment. The using of variety of ground cover plants as refugia area are expected to be an alternative habitat for pollinators insect in plants: Cyperus rotundus L., Bidens pilosa L., Commelina difussa L., Capsicum frutescens L., and Ageratum conyzoides L. Observations made by "visual control". This reseacch aims to know the composition of pollinators insect visit of ground cover plants and analyze their patterns. Analysis of the data structure of insect communities in the spring and the fruit season obtained from INP and diversity (Shannon-Winner Index). Parameters are compared to diversity and abundance with ANOVA test, composition using Morisita Index. The results show that the abundance of insect pollinators of spring higher at 7 families (31%) with H '= 1.698 instead of the fruit season is 6 families (25%) with H' = 1.600. Abundance and diversity of pollinators insect in the spring and fruit season with a significance of P < 0.05. Morisita similarity index of 82%. Analysis of environmental factors of temperature, humidity, and light intensity on the abundance of insect pollinators found positive correlation with R-square 87.5%.

Use of the foraging area by captive bred oriental storks (Ciconia boyciana) in a closed semi natural paddy field

Rice paddy fields have been recognized as an alternative habitat for avian wetland foragers, and fish-rice farms have become a new tool in improving the abundance of aquatic animals. However, the use of the habitats by avian foragers, particularly by oriental storks (<TEX>$Ciconia$</TEX> <TEX>$boyciana$</TEX>), was not well understood. In the present study, we investigated how a fish-rice farm influenced the abundance of aquatic animals and documented the foraging behavior of the two captive bred oriental storks in a closed semi-natural paddy field. Our results showed that the fish refuge pond (water depth 40 cm) had a higher abundance of fish whereas the areas planted with rice (water depth 20 cm) had more tadpoles and some aquatic insects. The two captive bred oriental storks captured mostly fish and aquatic insects in the rice-planted area and mostly fish in the fish refuge pond. The two oriental storks had higher foraging success and spent more time for foraging in the rice-planted area than in the fish refuge pond. This result suggests that the oriental storks might prefer foraging in the area with fish, aquatic insects, and amphibians under a greater success rate presumably due to shallow water depth in the paddy fields with a fish-rice farm.

A theoretical framework for understanding the ecology and conservation of bamboo-specialist birds

Worldwide, populations of a diverse array of bamboo-specialist birds must respond to the life cycles of typical woody bamboos, which include a long vegetative phase, a short period in sexual reproduction (seeding), and a short period dead. While some bamboo species flower continuously in time, but scattered in space, over different parts of their distribution, others exhibit a single, synchronized mass-seeding event, followed by death over hundreds of square kilometers. Thus, bamboo-specialist birds experience extreme variability in their habitat and food sources, and may pass from a period of overabundant habitat and food resources to a period of extreme resource scarcity. At a community level, bamboo species are out of phase with each other. Masting events of several bamboo species may coincide one cycle, but not the next. The resulting long-term dynamics of bamboo cycles at a community scale will result in a temporal and geographic mosaic of resource availability over very long periods of time, where the initial conditions that any bird experienced may occur only sporadically over centuries and very large regions. We aim to propose a theoretical framework for understanding the population ecology of bamboo-specialist birds and discuss implications for their conservation. Three main diet and life-history strategies of bamboo-specialist birds can be identified based on their natural history. First, insectivorous bamboo specialists that inhabit woody bamboos may be relatively sedentary during the long vegetative growth phase, but they must experience population declines, switch to alternative habitat, or travel widely during bamboo die-off events. They benefit from long-term habitat stability but must face short-term reductions in habitat that do not affect all generations of birds. Second, bamboo seed specialists must rely on an ephemeral source of food available only after large intervals of time at most locations. Since bamboo cycles are typically much longer than the lives of individual birds, there is no chance for seed-specialist birds to learn when and where bamboo seeds will be available in the future. Thus, although bamboo seed availability is ecologically predictable (i.e., seeds are always available after the same length of time at a given place), seed availability is unpredictable to individual birds. During their lifetime, most individual bamboo seed-specialists must face a lack of their preferred food supply, at which time they must wander to survive. And third, mixed strategists usually feed on bamboo shoots, leaves, and insects, but consume bamboo seeds when available. Their life history combines elements of both previous categories: they can benefit from long-term habitat stability like insectivores, and take advantage of masting events like seed specialists. Niche width (degree of specialization) in conjugation with the long-term dynamics of bamboo cycles should determine the degree of nomadism and amplitude of bamboo-specialist population cycles. Nomadism appears to be distributed along a continuum from the temporarily nomad insectivores and mixed strategists to the local and regional nomadic seed specialists. A protected area cannot shelter healthy populations of the most specialized bamboo-seed specialists because they track temporally and spatially unpredictable resources over large temporal and spatial scales. Overall, to effectively protect this ecological system, it is crucial to conserve a network of natural areas capable of providing bamboo in different phases and at different times and places, as well as subsidiary food resources that will allow birds to move away from bamboo patches as they become unsuitable to new, suitable patches.

Adaptation to Aridity in the Malaria Mosquito Anopheles gambiae: Chromosomal Inversion Polymorphism and Body Size Influence Resistance to Desiccation

Chromosomal inversions are thought to confer a selective advantage in alternative habitats by protecting co-adapted alleles from recombination. The frequencies of two inversions (2La and 2Rb) of the afro-tropical malaria mosquito Anopheles gambiae change gradually along geographical clines, increasing in frequency with degree of aridity. Such clines can result from gene flow and local selection acting upon alternative karyotypes along the cline, suggesting that these inversions may be associated with tolerance to xeric conditions. Since water loss represents a major challenge in xeric habitats, it can be supposed that genes inside these inversions are involved in water homeostasis. To test this hypothesis, we compared the desiccation resistance of alternative karyotypes from a colonised 2Rb/2La polymorphic population of A. gambiae from Cameroon. The strain included only the molecular form S, one of the genetic units marking incipient speciation in this taxon. Day-old mosquitoes of both sexes were assayed individually for time to death in a dry environment and the karyotype of each was determined post-mortem using molecular diagnostic assays for each inversion. In agreement with expectations based on their eco-geographical distribution, we found that 2La homokaryotypes survived significantly longer (1.3 hours) than the other karyotypes. However, there was weak support for the effect of 2Rb on desiccation resistance. Larger mosquitoes survived longer than smaller ones. Median survival of females was greater than males, but the effect of sex on desiccation resistance was weakly supported, indicating that differential survival was correlated to differences between sexes in average size. We found weak evidence for a heterotic effect of 2La karyotype on size in females. These results support the notion that genes located inside the 2La inversion are involved in water balance, contributing towards local adaptation of A. gambiae to xeric habitats, beyond the adaptive value conferred by a larger body size.

Wright's Shifting Balance Theory and the Diversification of Aposematic Signals

Despite accumulating evidence for selection within natural systems, the importance of random genetic drift opposing Wright's and Fisher's views of evolution continue to be a subject of controversy. The geographical diversification of aposematic signals appears to be a suitable system to assess the factors involved in the process of adaptation since both theories were independently proposed to explain this phenomenon. In the present study, the effects of drift and selection were assessed from population genetics and predation experiments on poison-dart frogs, Ranitomaya imitator, of Northern Peru. We specifically focus on the transient zone between two distinct aposematic signals. In contrast to regions where high predation maintains a monomorphic aposematic signal, the transient zones are characterized by lowered selection and a high phenotypic diversity. As a result, the diversification of phenotypes may occur via genetic drift without a significant loss of fitness. These new phenotypes may then colonize alternative habitats if successfully recognized and avoided by predators. This study highlights the interplay between drift and selection as determinant processes in the adaptive diversification of aposematic signals. Results are consistent with the expectations of the Wright's shifting balance theory and represent, to our knowledge, the first empirical demonstration of this highly contested theory in a natural system.