Wood ingestion by passalid beetles in the presence of xylose-fermenting gut yeasts

During a survey of insect gut micro-organisms, we consistently isolated Pichia stipitis-like yeasts (Fungi: Ascomycota, Saccharomycetes) from the wood-ingesting beetles, Odontotaenius disjunctus and Verres sternbergianus (Coleoptera: Passalidae). The yeasts were isolated from passalid beetles over a wide area, including the eastern and midwestern USA and Panama. Phylogenetic analyses of the nuclear encoded small and large subunit rRNA gene (rDNA) sequences distinguished a well-supported clade consisting of the passalid yeasts and Pichia stipitis, P. segobiensis, Candida shehatae and C. ergatensis. Members of this clade have the ability to ferment and assimilate xylose or to hydrolyse xylan, major components of the polysaccharide, hemicellulose. Sexual reproduction was present in the passalid isolates but was rare among the gut yeasts of other beetles to which they were compared. Minor genetic and phenotypic variation among some of the passalid yeasts was detected using markers from the internal transcribed spacer region of the rDNA repeat unit, morphology, and in vitro metabolic tests. The consistent association of xylose-fermenting yeasts of almost identical genotypes with passalid beetles across a broad geographical distribution, suggests a significant symbiotic association.     

Desiccation resistance and water balance in southern African keratin beetles (Coleoptera, Trogidae): the influence of body size and habitat

Desiccation resistance and water balance were examined in the adults of seven trogid species, which differed both in body size and in the habitats from which they were collected. Body water contents (51–58% fresh mass) and desiccation rates at 27 °C (0.00026–0.00093 g h⁻¹) in these species were very similar to those of unrelated, similar-sized beetles from arid habitats. The keratin beetles differed markedly from many other adult Coleoptera by virtue of their very high haemolymph osmolality and inability to regulate haemolymph osmolality, and to catabolise lipids for water production, during desiccation. Like most other insects, the xeric trogid species had lower rates of water loss and longer survival times than trogids from mesic areas. This was due both to lower rates of water loss and to the larger body size of species from the more arid areas. Because absolute body water content was higher in large beetles than in small ones, larger body size conferred higher desiccation resistance on the very large Kalahari desert species. This suggests that there may be strong selection for large body size in such insects from arid areas. Most ecological and ecophysiological investigations of geographical variation in body size, and the species-body size distribution, have focused on temperature and metabolic rate as explanatory variables. This study suggests that attention should also be given to desiccation resistance. Accepted: 29 September 1997     

The mitogenomes of three beetles (Coleoptera: Polyphaga: Cucujiformia): New gene rearrangement and phylogeny

The mitochondrial genome (mitogenome) has been extensively used for studying phylogenetic relationships at different taxonomic levels. Several molecular analyses have been performed, but the phylogenetic relationships among infraorders in Polyphaga have not been well resolved. In this work, three nearly complete mitogenomes of Coleoptera, Sitophilus oryzae, Oryzaephilus surinamensis and Callosobruchus chinensis, were determined. The O. surinamensis and S. oryzae mitogenomes harbor gene content typical of other Polyphaga mitogenomes, while a gene rearrangement (trnQ) was found in the C. chinensis mitogenome. The mitogenomes of these three Coleoptera species each consist of approximately 13 protein-coding genes, 22 tRNA genes, two rRNA genes and one A + T-rich region. Phylogenetic analysis within Polyphaga was carried out based on mitochondrial data. The phylogenetic results within Polyphaga support the basal position of Cyphon sp., which belonged to Scirtoidea, Elateriformia. Within Cucujiformia, monophyletic Curculionoidea, Chrysomeloidea and Tenebrionoidea were confirmed.     

白蚁肠道共生微生物的作用:酵母,一个“隐身”的特别菌群

长期以来,白蚁对木质纤维素的降解能力令人惊叹,毫无疑问,其在全球碳循环中扮演着一个十分重要的角色。这一强大功能的实现极大地依赖于一种特别的肠道"消化液(digestome)",它的构成不仅包括了来自白蚁自身产生的木质纤维素降解酶系统,还来源于独特与多样的肠道共生微生物的贡献(包括了古细菌、细菌、酵母以及其他真核生物),它们的协同作用能有效地将木质纤维素生物质高效转化为乙酸、甲烷、二氧化碳、氢气等物质。然而,到目前为止,我们对这类昆虫的独特肠道生物转化系统的认识还很不深入,特别是针对肠道内的那些各类共生微生物菌群的功能、白蚁与共生微生物间的相互关系、以及潜在的科学与应用价值还无法给予明确的科学解释,更不用说针对其肠道中的共生酵母菌群,一类通常被忽略的独特微生物。近20多年来,越来越多的研究证据表明,白蚁肠道共生酵母在与寄主的关系中表现了不可或缺的重要性与独特功能,已被证明广泛分布于不同白蚁及许多其他昆虫的肠道中。随着近20年来越来越多昆虫肠道共生微生物酵母群被发现和鉴定,他们潜在的功能以及与寄主的共生机制被逐步解析,这些研究结果进一步揭示了"隐身"的昆虫肠道酵母类微生物菌群与寄主的营养、关键生物质转化过程中的重要酶系统、转化过程中的关键中间产物的转化与利用、抵御外源性的重要病原物,甚至对白蚁种群繁衍的远缘交配等方面均可能发挥了重要和不可缺少的作用。本文将试图归纳相关研究的最新进展,系统总结与解析白蚁肠道来源共生酵母的重要科学价值及其在不同领域的潜在应用前景。     

Intestine length in the fishes of a tropical stream: 2. Relationships to diet — the long and short of a convoluted issue

Synopsis We examined the relationship between the intestine length and the amount of plant material in the diet of 21 species of fish from forest streams in Panama. Alimentary tract analyses supplemented by literature reports showed that four loricariid catfish species and one poeciliid were specialized herbivores consuming almost exclusively periphyton and detritus. Four species, including one erythrinid, one characid, one trichomyctycterid and one eleotrid, were carnivores consuming almost entirely food of animal origin. Twelve species, including five characids, one lebiasinid, two pimelodelids, three cichlids and one poeciliid, were omnivores consuming food of both plant and animal origin, but the average proportion of food of plant origin (detritus and algae plus higher plant parts) varied from 4–60%. Most omnivores increased plant food consumption with increasing size. Because intestine length increases allometrically with body size and the pattern of increase differs considerably among species and is influenced by length:mass relationships, we compared species at the same size and took both length and mass into account. At a given size, intestine lengths of herbivores were longer than those of omnivores, and these were longer than those of carnivores. Differences in intestine length among the dietary categories were greater at larger body sizes and when the common size was defined by body mass than when it was defined by body length. There was no trend for the average proportion of plant material consumed to be related to intestine length among the omnivores, when confounding effects of body mass were taken into account. The slopes of the allometric equations relating log₁₀ intestine length to log₁₀ body size for herbivores tended to be higher than for omnivores and higher for omnivores than for carnivores, but both herbivores and omnivores showed extensive variation and overlap with the other dietary categories. Among the omnivores, there was no trend for slopes to be steeper for species consuming more plant material on average or for species showing larger ontogenetic increases in plant consumption. These results permit increased precision in describing diet-intestine length relationships, but indicate that the widely held belief that intestine length reflects diet in fishes should only be applied to broad dietary categories and not to finer divisions among omnivores.     

The blood-brain barrier: connecting the gut and the brain

The BBB prevents the unrestricted exchange of substances between the central nervous system (CNS) and the blood. The blood-brain barrier (BBB) also conveys information between the CNS and the gastrointestinal (GI) tract through several mechanisms. Here, we review three of those mechanisms. First, the BBB selectively transports some peptides and regulatory proteins in the blood-to-brain or the brain-to-blood direction. The ability of GI hormones to affect functions of the BBB, as illustrated by the ability of insulin to alter the BBB transport of amino acids and drugs, represents a second mechanism. A third mechanism is the ability of GI hormones to affect the secretion by the BBB of substances that themselves affect feeding and appetite, such as nitric oxide and cytokines. By these and other mechanisms, the BBB regulates communications between the CNS and GI tract.     

Habitat use,abundance, and persistence of Neotropical migrant birds in a habitat matrix in northeast Belize

ABSTRACT To ensure adequate protection of nonbreeding habitats used by Neotropical migratory landbirds, we must first address questions about habitat use and quality. On the Yucatan peninsula, migrants use many habitats, several of which remain unstudied, and methodological differences preclude interhabitat comparisons based on studies to date. We used distance sampling along line transects in six habitats in northeast Belize to examine use of previously unstudied habitats (e.g., salt marsh) by Neotropical migrants and to permit comparison across habitats. We calculated unadjusted and adjusted (for detectability) density estimates for individual migrant species and for all species combined to generate hypotheses about habitat quality based on the assumption that density and quality are positively correlated. Adjusted density estimates for all migrants were highest in black mangrove habitat (1799 ± 110 ind/km²), intermediate in three forest types and milpa (range 598–802 ind/km²), and lowest in salt marsh (207 ± 32.3 ind/km²). By combining density estimates with habitat availability in our study region, we estimated that evergreen forest and black mangrove supported 70% and 9% of the region's migrant population, respectively. At the species level, five of the 10 most common species had habitat preferences (>50% detections in one habitat). Given the diversity of habitat preferences among species and apparent seasonal movements, our results indicate that Neotropical migrants in northeast Belize are dependent on a matrix of interconnected habitats.     

Intestine length in the fishes of a tropical stream: 1. Ontogenetic allometry

Synopsis We examined the ontogenetic allometry of intestine length in relation to body length and body mass in 21 species of fish from forest streams in Panama. The relationships between log₁₀ intestine length and log₁₀ body length and mass were well described by linear regressions, although some species showed slight curvilinearity. Slopes and intercepts of the linear regressions varied considerably among species. Intestine length was positively allometric in most species, with slopes of the intestine length:body length relationship ranging from 1.09 to 2.11. Relative intestine lengths (intestine length/body length) varied by two orders of magnitude (0.39–38.44) in the data set as a whole, but the variation was about one order of magnitude when species were compared at a common body size. Species in which body mass increased more rapidly with body length had more rapid increases in intestine length with body length. Among omnivorous and carnivorous species compared at the same body length, heavier species had longer intestines. Interspecific comparisons of relative intestine length may produce misleading conclusions unless comparisons are made at a common size and account for differences in relative mass.     

The FORMNET‐B database: monitoring the biomass and dynamics of disturbed and degraded tropical forests

The biomass and dynamics of disturbed and degraded tropical forests have mostly been ignored in the recent scientific literature, partly because of a spotlight on old‐growth forests but also due to a lack of long‐term data from degraded forests. There is a pressing need to understand the rates and patterns of growth, mortality and recruitment in degraded forests, not only because they are increasing in area relative to old‐growth forests, but also due to their potential capacity to sequester large amounts of carbon dioxide from the atmosphere. This paper introduces a permanent forest plot network and database, FORMNET‐B (GIVD ID# NA‐BZ‐001), designed to study the long‐term dynamics of disturbed and degraded tropical forests in Belize, Central America.     

肠道微生物与神经及精神疾病的研究现状

近年来随着微生物16S rRNA、高通量测序以及序列识别技术的成熟,肠道微生物与多种疾病相关性的研究呈蓬勃发展。大量的研究证据表明肠道微生物可通过刺激迷走神经、调节下丘脑‒垂体‒肾上腺轴功能、参与调节机体免疫系统、合成分泌神经递质、产生多种自身代谢产物（如短链脂肪酸、Lipid456、BDNF等小分子物质）机制参与中枢神经系统自身免疫性疾病、癫痫、神经变性疾病、抑郁症、自闭症、精神分裂症的发病过程。研究肠道微生物与中枢神经系统疾病的相互作用,为揭示复杂的中枢神经系统疾病以及精神疾病的发病机制提供科学证据,以期通过调解肠道菌群的微环境治疗神经精神类疾病。     

Monitoring arthropods in a tropical landscape: relative effects of sampling methods and habitat types on trap catches

To discuss the challenge of monitoring multi-species responses of tropical arthropods to disturbance, we considered a large dataset (4 × 10⁵ individuals; 1,682 morphospecies representing 22 focal taxa) based on the work of parataxonomists to examine the effects of anthropogenic disturbance on arthropods at Gamba, Gabon. Replication included three sites in each of four different stages of forest succession and land use after logging, surveyed during a whole year with four sampling methods: pitfall, Malaise, flight-interception and yellow pan traps. We compared the suitability of each sampling method for biological monitoring and evaluated statistically their reliability for 118 arthropod families. Our results suggest that a range of sampling methods yields more diverse material than any single method operated with high replication. Multivariate analyses indicated that morphospecies composition in trap catches was more strongly influenced by habitat type than by sampling methods. This implies that for multi-species monitoring, differences in trap efficiency between habitats may be neglected, as far as habitat types remain well contrasted. We conclude that for the purpose of monitoring large arthropod assemblages in the long-term, a protocol based on operating a set of different and non-disruptive traps appears superior in design than summing a series of taxa-specific protocols.     

Systematic revision of Neotropical Achalcus and a related new genus (Diptera: Dolichopodidae, Achalcinae) with comments on their phylogeny, ecology and zoogeography

A revision of the species of the subfamily Achalcinae of the Neotropical region is presented. A new genus, Australachalcus gen. nov. , is erected based on the presence of six dorsocentral bristles and synapomorphies in the hypopygium. Eight new Achalcus species ( bilineatus , brevicornis , costaricensis , cyanocephalus , maculipennis , micromorphoides , niger , tibialis ) and eight new Australachalcus species ( acornis , browni , cummingi , incisicornis , pseudorobustus , robustus , setosus , variabilis ) are described, and Achalcus albipalpus Parent, A. brevinervis Van Duzee, A. longicornis Van Duzee and Enlinia edwardsae (Van Duzee) are newly referred to Australachalcus and redescribed. A key to males of all species and females of eight species is provided. One Palaearctic species, Achalcus melanotrichus Mik, and nine New Zealand Achalcus species ( chaetifemoratus , luteipes , medius , minor , minusculus , minutus , nigroscutatus , relictus , separatus ) described by Parent are also transferred to Australachalcus . In Neotropical Achalcinae, three Achalcus and more than four different Australachalcus species groups can be distinguished, whereas all Holarctic Achalcus species belong to the single A. flavicollis species group. In the Neotropics, Australachalcus is nearly entirely confined to Chile, whereas Achalcus is recorded from Costa Rica, Venezuela, Ecuador, Colombia, Peru and Chile, with no or little overlap in distribution between the separate species groups. Beyond Chile, most achalcine species treated here were collected at higher altitudes. Most Chilean species are only active during the southern summer, whereas in Costa Rica achalcine representatives are encountered throughout the year.  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 143 , 27–73.     

The genus Spathius Nees (Hymenoptera,Braconidae, Doryctinae) in Mexico: occurrence of a highly diverse Old World taxon in the Neotropics

Two new species of the parasitoid wasp genus Spathius Nees (Braconidae: Doryctinae) from Mexico, S. mexicanus sp. n. and S. chamelae sp. n., are described and illustrated. These represent the second and third described species of this highly diverse Old World genus in the Neotropics, and the first described species recorded for the Mexican territory.     

The influence of habitat heterogeneity and latitude on gamma diversity of the Nearctic Simuliidae,a ubiquitous group of stream‐dwelling insects

Among the most prominent, large‐scale patterns of species richness are the increases in richness with decreasing latitude and with increasing habitat heterogeneity. Using the stream‐dwelling larval and pupal stages of North American black flies (Diptera: Simuliidae), we address 3 broad questions about species richness: (i) Does a significant latitude–richness relationship exist? (ii) How does habitat heterogeneity influence gamma diversity? (iii) What is the sign (positive or negative) of the latitude–richness and the heterogeneity–richness relationships? We found no evidence that habitat heterogeneity influences gamma diversity. The estimated peak species richness for black flies in North America was at 50–53°N, which also corresponds with peak generic richness. All plesiomorphic, extant lineages of the Simuliidae in the Western Hemisphere are found in cool mountainous environments of North America, suggesting that peak richness at 50–53°N might be a signature of this phylogenetic pattern and a reflection of underlying historical processes.     

Phylogeography of the livebearer Xenophallus umbratilis (Teleostei: Poeciliidae): glacial cycles and sea level change predict diversification of a freshwater tropical fish

The biogeography of Central America is viewed as a classic case study in understanding the impact of vicariant events on patterns of biotic dispersal. While many biogeographers have focused on community composition and geographical limits of species at broad scales across Central America, much less work has focused on post-colonization diversification patterns at finer scales. The livebearing freshwater fish Xenophallus umbratilis presents an ideal system for determining the impact of recent Earth history events on biodiversity in northern Costa Rica. Here, we test the hypotheses that marine inundation of the San Carlos and northern Limón basins during the Pliocene and Pleistocene has caused genetic fragmentation among X. umbratilis populations, despite contemporary freshwater connections. To test this idea, we collected mitochondrial (cytochrome b ) sequence data in 162 individuals taken from 27 localities across northern Costa Rica. We employed a variety of analytical approaches, including: maximum parsimony and maximum likelihood, analysis of molecular variance, and demographic analysis of population size through time. We found four major clades within X. umbratilis , each geographically isolated with no shared haplotypes across drainages. Oddly, clades that occupy adjacent drainages are not always sister taxa in the phylogeny, suggesting that colonization in this species is more complex than a simple model of isolation by distance. All our results are consistent with the hypothesis that changes in sea level associated with glacial eustatic cycles have had an important effect in shaping diversification patterns in this species.     

The role of tropical dry forest as a long-term barrier to dispersal: a comparative phylogeographical analysis of dry forest tolerant and intolerant frogs

We used a comparative phylogeographical approach to investigate the origins of the disjunct wet forest biota of the Golfo Dulce region along the Pacific slope of Costa Rica. This region is isolated by Pacific dry forests north and south and isolated from Caribbean wet forests by mountains. We studied three sympatric lowland frog species in the Craugastor fitzingeri species group that prefer wet forest but differ in their response to dry habitats. In dry forest, C. fitzingeri can survive along streams while C. crassidigitus and C. talamancae are entirely absent. We collected samples from across the ranges of all three species, and obtained mitochondrial DNA sequence data from the COI and cytochrome b genes. We observed significant phylogeographical structure in C. crassidigitus and C. talamancae, but much less in C. fitzingeri, demonstrating that mountain barriers and dry forest habitat have reduced mitochondrial gene flow in the strictly wet-forest species. Additionally, we discovered that the Golfo Dulce and Central Panama populations of C. crassidigitus appear to have diverged in the Pliocene or earlier, suggesting that the dry forest separating these populations is old. Our phylogenetic analysis of 12 of approximately 16 species of the C. fitzingeri species group suggests that the three lowland species are each other's closest relatives. Because of this shared phylogenetic history, we attribute the striking differences in phylogeographical structure to the different ecologies of the frogs. In summary, we find that what appear to be minor differences in the natural history of these three closely related species may profoundly impact the potential for dispersal, range size, and cladogenesis.     

Green sloths and brown cows: the role of dominant mammalian herbivores in carbon emissions for tropical agro‐ecosystems

When Neotropical forests are cleared, there is a rapid switch in the dominant herbivore from wild sloths (suborder Folivora) to domestic cows Bos taurus. We quantified carbon dynamics for these mammals and the ecosystems they inhabit. Because of their low metabolic rates and photosynthetically‐active algae, sloths emit trivial amounts of carbon (12 g C/sloth*day) compared to cows (2.3 kg C/cow*day). In parallel, forests are carbon sinks (?242 g C/m²*year) and pastures sources (261 g C/m²*year); cows contribute >50% of the net emissions from pastures. For a small farm in Costa Rica, this turnover in herbivores translates into ~166 metric tonnes of additional C emitted annually.     

Random movement pattern of fed and unfed adult Colorado potato beetles in bare‐ground habitat

• 1 Although the successful management of the Colorado potato beetle Leptinotarsa decemlineata (Say) depends on the prevention of its dispersal, its walking pattern in the landscape remains poorly understood. In the present study, post‐diapause, early summer, late summer and colony adult beetles, both fed and unfed before release, were tracked with a harmonic radar to establish their walking movement pattern in a bare‐ground field.
• 2 The random walk model successfully described the dispersal of all beetle types, whether fed or unfed.
• 3 The diverse life history of this species was manifested by an increased distance travelled and deviations of individual paths from the random model. Starved post‐diapause beetles travelled furthest and individual paths deviating from random were both local and directed, probably aiming to maximize opportunities for host colonization. Starved early summer beetles also travelled further than fed beetles but relied more on random movement to disperse in the habitat. Starving had little impact on the distance travelled or the path deviations of late summer beetles that are searching for overwintering site rather than hosts.
• 4 The increased displacement of starving beetles over fed beetles corresponded with an increased walking step and index of straightness.
• 5 The impact of starvation on travel distance was greater than expected from laboratory tests.
• 6 In conclusion, the results obtained in the present study suggest a random walking pattern to search arable land until host volatile or visual impulses trigger a more directed walk or flight.