Ant cues affect the oviposition behaviour of fruit flies (Diptera: Tephritidae) in Africa

Abstract. Although most studies on fruit fly oviposition behaviour focus on horizontal interactions with competitors and cues from host plants, vertical interactions with predators are poorly documented. The present study provides direct evidence indicating that the oviposition behaviour of the two main mango fruit fly species, Ceratitis cosyra (Walker) and Bactrocera invadens Drew‐Tsurata & White, is affected by secretions of the dominant arboreal ant Oecophylla longinoda (Latreille). When offered ant‐exposed and unexposed mangoes in the absence of the ants, both fly species are reluctant to land on ant‐exposed fruits and, when having landed, often take off quickly and fail to oviposit. The number of puparia collected from unexposed mangoes is approximately eight‐fold higher than from ant‐exposed ones. The results obtained from laboratory experiments and field observations confirm that adult fruit flies are more affected through repellence by ant cues than by direct predation. The use of cues by fruit flies in predator avoidance has implications for evolutionary ecology, behavioural ecology and chemical ecology.     

Discongruence of Mhc and cytochrome b phylogeographical patterns in Myodes glareolus (Rodentia: Cricetidae)

In the present study, a phylogeographical approach was developed to analyse the influence of selection and history on a major histocompatibility complex (Mhc) class II gene polymorphism in European bank vole (Myodes glareolus) populations. We focused on exon 2 of the Dqa gene because it is highly variable in a large array of species and appears to evolve under pathogen‐mediated selection in several rodent species. Using single‐strand conformation polymorphism analysis and sequencing techniques, 17 Dqa‐exon2 alleles, belonging to at least two different copies of Dqa gene, were detected over the distribution range of M. glareolus. Evidence of selection was found using molecular and population analyses. At the molecular level, we detected 13 codons evolving under positive selection pressures, most of them corresponding to regions coding for putative antigen binding sites of the protein. At the European level, we compared patterns of population structure for the Dqa‐exon2 and cytochrome b (cyt b) gene. We did not detect any spatial genetic structure among M. glareolus populations for the Dqa‐exon2. These results strongly differed from those obtained using the cyt b gene, which indicated a recent phylogeographical history closely linked to the last glacial events. Seven mitochondrial lineages have yet been described, which correspond to major glacial refugia. Altogether, our results revealed clear evidence of balancing selection acting on Dqa‐exon2 and maintaining polymorphism over large geographical areas despite M. glareolus history. It is thus likely that Mhc phylogeographical variability could have been shaped by local adaptation to pathogens. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 881–899.     

The impact of red howler monkey latrines on the distribution of main nutrients and on topsoil profiles in a tropical rain forest

Scarcity of organic matter and nutrients in the topsoil is a typical feature of lowland primary tropical rain forests. However, clumped defecation by vertebrate herbivore troops and further dung beetle processing may contribute to locally improve soil biological activity and plant growth. We studied the impact of clumped defecation by the red howler monkey (Alouatta seniculus), a frugivorous primate, on the vertical distribution of topsoil (0–6 cm) main nutrients and microstructures in a tropical rain forest (French Guiana). Three latrines, where monkey troops regularly defecate, were sampled, together with adjoining controls for carbon, nitrogen, phosphorus and microscopic components. The vertical distribution of C and N was affected by clumped defecation: nutrients were mostly restricted to the top 2 cm in control areas while latrines exhibited homogeneously distributed C and N, resulting in higher C and N content below 2 cm. No marked effect of defecation was registered on Olsen P. A small although significant increase in pH (0.1–0.3 pH units) and a marked increase in soil respiration (×1.5–2.5) were registered in latrines. Soil microstructures were studied by the small‐volume method. Variation according to depth, site and clumped defecation was analysed by Redundancy Analysis. The three latrines were characterized by an increase in root‐penetrated mineral‐organic assemblages, mainly composed of recent and old earthworm faeces. The local stimulation of plant roots, microbial and earthworm activity was prominent, together with an increase in soil fertility. Consequences for the regeneration of tropical rain forests in the Amazonian basin were discussed, in the light of existing knowledge.     

Hydrological connectivity drives patterns of macroinvertebrate biodiversity in floodplain rivers of the Australian wet /dry tropics

1. Floodplain rivers in Australia's wet/dry tropics are regarded as being among the most ecologically intact and bio-diverse lotic ecosystems in the world, yet there have been relatively few community-based studies of their aquatic fauna.
2. To investigate relationships between hydrological connectivity and biodiversity in the region, macroinvertebrates were collected from sites within two contrasting floodplain rivers, the 'tropical' Gregory River and 'dryland' Flinders River systems, during the dry season and analysed at various spatial scales. A subset of sites was re-sampled in the following dry season to explore temporal variation. The fauna consisted of 124 morphotaxa, dominated by gatherers and the Insecta.
3. As predicted, hydrological connectivity (the lotic or lentic status of waterbodies) had a major influence on macroinvertebrate assemblage composition and diversity, both in space and time. Assemblages from waterbodies with similar connection histories were most alike, and beta-diversity between assemblages was greatest between lotic and lentic waterbodies, tending to increase with increasing spatial separation.
4. At smaller spatial scales, a number of within-waterbody, habitat and water quality characteristics were important for explaining variation (61%) in the taxonomic organization of assemblages, and characteristics associated with primary productivity and habitat diversity were important for explaining variation (45%) in the functional organization of assemblages. However, much of the small-scale environmental variation across the study region appeared to be related to broad-scale variation in hydrological connectivity, which had both direct and indirect effects on macroinvertebrate assemblages.
5. Conservation of the biodiversity in Australia's wet/dry tropics may depend on conserving the natural variation in hydrological connectivity and the unregulated flow of floodplain rivers.     

Survival and Body Condition of Raccoons at the Edge of the Range

ABSTRACT We investigated the influence of intrinsic and extrinsic variables on overwinter survival of raccoons (Procyon lotor; n = 114) at the northern edge of their distribution. A Cox proportional hazard model identified winter severity as the variable with the greatest influence on raccoon survival (β = 1.08). Autumn body condition estimates (20.5 ± 0.46% total body fat) were relatively stable across years even though we observed large differences in autumn food indices. Variations in autumn body condition did not explain heterogeneity observed in overwinter survival nor the spring condition in which raccoons emerged. Relatively constant autumn body condition suggests reliable availability of anthropogenic food resources may negate variations observed in natural food items on which raccoons rely during hyperphagia. Conversely, spring body condition did vary among years and was highly correlated with winter severity. Accordingly, we also observed a strong inverse relationship with overwinter survival and winter severity. Our findings indicate winter climatic constraints are important factors governing the northern limit of raccoon distribution and changes in winter severity could have important implications in further range expansion of this species.     

Inhibition of germination of dormant barley (Hordeum vulgare L.) grains by blue light as related to oxygen and hormonal regulation

Germination of primary dormant barley grains is promoted by darkness and temperatures below 20 °C, but is strongly inhibited by blue light. Exposure under blue light at 10 °C for periods longer than five days, results in a progressive inability to germinate in the dark, considered as secondary dormancy. We demonstrate that the inhibitory effect of blue light is reinforced in hypoxia. The inhibitory effect of blue light is associated with an increase in embryo abscisic acid (ABA) content (by 3.5‐ to 3.8‐fold) and embryo sensitivity to both ABA and hypoxia. Analysis of expression of ABA metabolism genes shows that increase in ABA mainly results in a strong increase in HvNCED1 and HvNCED2 expression, and a slight decrease in HvABA8′OH‐1. Among the gibberellins (GA) metabolism genes examined, blue light decreases the expression of HvGA3ox2, involved in GA synthesis, increases that of GA2ox3 and GA2ox5, involved in GA catabolism, and reduces the GA signalling evaluated by the HvExpA11 expression. Expression of secondary dormancy is associated with maintenance of high embryo ABA content and a low HvExpA11 expression. The partial reversion of the inhibitory effect of blue light by green light also suggests that cryptochrome might be involved in this hormonal regulation.     

The histological structure of the calcified lung of the fossil coelacanth Axelrodichthys araripensis (Actinistia: Mawsoniidae)

Abstract: The palaeohistological study of the calcified internal organ of Axelrodichthys araripensis Maisey, 1986, a coelacanthiform from the Lower Cretaceous of Brazil (Crato (Aptian) and Santana (Albian) formations of the Araripe Basin), shows that the walls of this organ consist of osseous blades of variable thickness separated from each other by the matrix. This indicates that, in the living individuals, the walls were reinforced by ossified plates, probably separated by conjunctive tissue. This calcified sheath present in Axelrodichthys, as well as in other fossil coelacanths, lies in ventral position relative to the gut and its single anterior opening is located under the opercle, suggesting a direct connection with the pharynx or the oesophagus. The calcified organ of Axelrodichthys, like that of other fossil coelacanths, is here regarded as an ‘ossified lung’ and compared with the ‘fatty lung’ of the extant coelacanth Latimeria. The reinforcement of the pulmonary walls by the overlying osseous blades could be interpreted as a means of adapting volumetric changes in the manner of bellows, a necessary function for ventilation in pulmonary respiration. Other functional hypotheses such as hydrostatic and/or acoustic functions are also discussed.     

Conflicts between feeding and reproduction in amphibious snakes (sea kraits,Laticauda spp.)

If reproduction impairs an organism's ability to perform other fitness‐related activities, natural selection may favour behavioural adjustments to minimize these conflicts. This is presumably the reason why many animals are anorexic during the breeding season. We studied amphibious sea snakes, a group whose ecology facilitates teasing apart the causal links between reproduction and feeding. In both Laticauda laticaudata and L. saintgironsi in New Caledonia, adult females cease feeding as their eggs develop. The advantages of foregoing feeding do not relate to thermoregulation (because foraging does not entail lower body temperatures), nor are they attributable to physical constraints on abdominal volume (because in a snake's linear body, there is little overlap between the stomach and the oviducts). Instead, female sea kraits appear to cease feeding because their bodily distension impedes locomotor ability, rendering them less effective at foraging and more vulnerable to aquatic predators.     

Understorey environments influence functional diversity in tank‐bromeliad ecosystems

1. A substantial fraction of the freshwater available in neotropical forests is impounded within the rosettes of bromeliads that form aquatic islands in a terrestrial matrix. The ecosystem functioning of bromeliads is known to be influenced by the composition of the contained community but it is not clear whether bromeliad food webs remain functionally similar against a background of variation in the understorey environment. 2. We considered a broad range of environmental conditions, including incident light and incoming litter, and quantified the distribution of a very wide range of freshwater organisms (from viruses to macroinvertebrates) to determine the factors that influence the functional structure of bromeliad food webs in samples taken from 171 tank‐bromeliads. 3. We observed a gradient of detritus‐based to algal‐based food webs from the understorey to the overstorey. Algae, rotifers and collector and predatory invertebrates dominated bromeliad food webs in exposed areas, whereas filter‐feeding insects had their highest densities in shaded forest areas. Viruses, bacteria and fungi showed no clear density patterns. Detritus decomposition is mainly due to microbial activity in understorey bromeliads where filter feeders are the main consumers of microbial and particulate organic matter (POM). Algal biomass may exceed bacterial biomass in sun‐exposed bromeliads where amounts of detritus were lower but functional diversity was highest. 4. Our results provide evidence that tank‐bromeliads, which grow in a broad range of ecological conditions, promote aquatic food web diversity in neotropical forests. Moreover, although bromeliad ecosystems have been categorised as detritus‐based systems in the literature, we show that algal production can support a non‐detrital food web in these systems.