Recent advances in understanding insect communities in tropical forests have contributed little to our knowledge of large-scale patterns of insect diversity, because incomplete taxonomic knowledge of many tropical species hinders the mapping of their distribution records. This impedes an understanding of global biodiversity patterns and explains why tropical insects are under-represented in conservation biology. Our study of approximately 500 species from three herbivorous guilds feeding on foliage (caterpillars, Lepidoptera), wood (ambrosia beetles, Coleoptera) and fruit (fruitflies, Diptera) found a low rate of change in species composition (beta diversity) across 75,000 square kilometres of contiguous lowland rainforest in Papua New Guinea, as most species were widely distributed. For caterpillars feeding on large plant genera, most species fed on multiple host species, so that even locally restricted plant species did not support endemic herbivores. Large plant genera represented a continuously distributed resource easily colonized by moths and butterflies over hundreds of kilometres. Low beta diversity was also documented in groups with differing host specificity (fruitflies and ambrosia beetles), suggesting that dispersal limitation does not have a substantial role in shaping the distribution of insect species in New Guinea lowland rainforests. Similar patterns of low beta diversity can be expected in other tropical lowland rainforests, as they are typically situated in the extensive low basins of major tropical rivers similar to the Sepik-Ramu region of New Guinea studied here.

Abstract. -The dorsal gill-arch musculature (DGM) Mugilomorpha + Atherinomorpha (= Percesoces Cope, 1875), Gasterosteomorpha, and. possibly, Centrisciformes (a pre-percomorph group, comprising only Centriscidae). Gasterosteomorpha includes a monophyletic Hypoptychidae {Hypoptychus + Aulichthys), Elassomatidae, Aulorhynchidae, monophyletic Synbranchiformes (Synbranchidae + Mastacembelidae), and Gasterosteidae, thus corroborating various hypotheses of Johnson and Patterson (1993) and Johnson and Springer (1997)

The jaw, suprahyoid, and extrinsic tongue muscles were studied in 11 genera, belonging to five tribes, of Old World squirrels. Significant variation in most of the adductor muscles is evident. The most primitive state of sciuromorphy is seen in the African tree squirrels Paraxerus and Funisciurus, especially as reflected in the anterior deep masseter. A derived state of sciuromorphy is found in five genera of Old World squirrels and perhaps evolved independently in each. Reduction of the temporalis muscle was observed in three genera, distantly related to one another. A unique arrangement of the superficial masseter is reported in the Asian giant tree squirrels, Ratufa. The arrangement of the masseter in the African pygmy squirrel, Myosciurus, is very similar to that of the South American pygmy squirrel, Sciurillus. We present hypotheses about the functional significance of these differences. In the derived state of sciuromorphy, which is found in three cases in squirrels that feed extensively on hard fruits, the anterior deep masseter is well positioned to increase the strength of the power stroke of the incisor bite. Among the pygmy squirrels, the position of the anterior deep masseter suggests that it plays a more significant role in molar chewing.

Comparative population genetics of ecological guilds can reveal generalities in patterns of differentiation bearing on hypotheses regarding the origin and maintenance of community diversity. Contradictory estimates of host specificity and beta diversity in tropical Lepidoptera (moths and butterflies) from New Guinea and the Americas have sparked debate on the role of host-associated divergence and geographic isolation in explaining latitudinal diversity gradients. We sampled haplotypes of mitochondrial cytochrome c oxidase I from 28 Lepidoptera species and 1,359 individuals across four host plant genera and eight sites in New Guinea to estimate population divergence in relation to host specificity and geography. Analyses of molecular variance and haplotype networks indicate varying patterns of genetic structure among ecologically similar sympatric species. One-quarter lacked evidence of isolation by distance or host-associated differentiation, whereas 21% exhibited both. Fourteen percent of the species exhibited host-associated differentiation without geographic isolation, 18% showed the opposite, and 21% were equivocal, insofar as analyses of molecular variance and haplotype networks yielded incongruent patterns. Variation in dietary breadth among community members suggests that speciation by specialization is an important, but not universal, mechanism for diversification of tropical Lepidoptera. Geographically widespread haplotypes challenge predictions of vicariance biogeography. Dispersal is important, and Lepidoptera communities appear to be highly dynamic according to the various phylogeographic histories of component species. Population genetic comparisons among herbivores of major tropical and temperate regions are needed to test predictions of ecological theory and evaluate global patterns of biodiversity. community ecology | DNA barcoding | phylogeography | plant-insect interactions | speciation

Predictability in the composition of tropical assemblages of insect herbivores was studied using a sample of 35,952 caterpillars (Lepidoptera) from 534 species, feeding on 69 woody species from 45 genera and 23 families in a lowland rainforest in Papua New Guinea. Caterpillar assemblages were strongly dominated by a single species (median 48% of individuals and 49% of biomass). They were spatially and temporally constant (median normalized expected species shared (NESS) similarity between assemblages from the same host was greater than or equal to 0.85 for three sites 8-17 km apart as well as for three four-month periods of the year). Further, the median presence of species was 11 months per year. Assemblages on hosts from different families and genera were virtually disjunct (NESS similarity less than 0.05) as the caterpillars were mostly specialized to a single plant family (77% of species) and, within families, to a single genus (66% of species), while capable of feeding on multiple congeneric hosts (89% of species). The dominance of caterpillar assemblages by a small number of specialized species, which also exhibited low spatial and temporal variability, permitted robust and reliable estimates of assemblage composition and between-assemblage similarity from small samples, typically less than 300 individuals per host plant. By contrast, even considerably larger samples were insufficient for estimates of species richness. A sample of 300 individuals was typically obtained from 1,050 m(2) of foliage sampled during 596 tree inspections (i.e. a particular tree sampled at a particular time) in the course of 19 sampling days (median values from 69 assemblages). These results demonstrate that, contrary to some previous suggestions, insect herbivore assemblages in tropical rainforests have a predictable structure and, as such, are amenable to study.

Anatomical differences among squirrels are usually most evident in the comparison of flying squirrels and nongliding squirrels. This is true of wrist anatomy, probably reflecting the specializations of flying squirrels for the extension of the wing tip and control of it during gliding. In the proximal row of carpals of most squirrels, the pisiform articulates only with the triquetrum, but in flying squirrels there is also a prominent articulation between the pisiform and the scapholunate, providing a more stable base for the styliform cartilage, which supports the wing tip. In the proximal wrist joint, between these carpals and the radius and ulna, differences in curvature of articular surfaces and in the location of ligaments also correlate with differences in degree and kind of movement occurring at this joint, principally reflecting the extreme dorsal flexion and radial deviation of the wrist in flying squirrels when gliding. The distal wrist joint, between the proximal and distal rows of carpals, also shows most variation among flying squirrels, principally in the articulations of the centrale with the other carpal bones, probably causing the distal row of carpal bones to function more like a single unit in some animals. There is little variation in wrist musculature, suggesting only minor evolutionary modification since the tribal radiation of squirrels, probably in the early Oligocene. Variation in the carpal bones, particularly the articulation of the pisiform with the triquetrum and the scapholunate, suggests a different suprageneric grouping of flying squirrels than previously proposed by McKenna (1962) and Mein (1970). J. Morphol. 246:85–102, 2000. Published 2000 Wiley‐Liss, Inc.

Aim This analysis of caterpillar (Lepidoptera) beta-diversity between tropical lowlands and highlands attempts to separate the effects of between-site ( 1 ) turnover of herbivore species on particular host plants, (2) changes in host use by herbivores, and (3) turnover of plant species on changes in herbivore assemblages.Location Two rain forest areas 130 km and 1700 altitudinal metres apart were studied in Papua New Guinea: one in the lowlands (100 m a.s.l.) on the northern coast of the island and one in the central New Guiñean cordillera at 1800 m a.s.l. MethodsThe analysis is based on caterpillar feeding records obtained by quantitative sampling and rearing of caterpillars from four Ficus species studied in the mountains and 21 Ficus species and 62 plant species from other genera and families studied in the lowlands, including three Ficus species studied in both areas. ResultsOnly 17% of species feeding on Ficus in the highlands also occurred in the lowlands. These species represented 1-46% of individuals in caterpillar assemblages on particular Ficus hosts. Widespread species included both Ficus specialists and generaUsts feeding on numerous plant famihes. Some of the Ficus speciahsts changed their preferred host species with altitude. High species turnover was not explained by changes in the species composition of host plants with altitude as lowland and montane assemblages feeding on the same Ficus species showed high turnover. Despite the rarity of widespread caterpillars, the lowland and montane Ficus assemblages were remarkably similar in their dominance structure, species richness, host specificity, generic composition and familial composition.Main conclusions PicMs-feeding Lepidoptera assemblages between tropical lowlands and highlands are characterized by substantial species turnover not explained by altitudinal changes in the composition of the vegetation. Further, species-rich plant genera can support caterpillar assemblages with relatively low beta-diversity compared with species-poor genera as caterpillars can switch their host preferences from one congeneric host species to another along an altitudinal gradient. Closely related plant species can thus represent a broad, continuously distributed resource along such gradients.

Abstract. 1. Caterpillar assemblages feeding on two alien plants, Piper aduncum and P. umbellatum, were studied in lowland rainforest in Papua New Guinea and compared with assemblages from 69 species of native woody hosts, including congeneric P. macropiper.2. Species richness of caterpillars feeding on P. aduncum (29 species per 1500 m^ of foliage) and P. umbellatum (36 species) was higher than the median richness for the 69 native hosts (23 species).3. The probability that a caterpillar species colonised alien Piper increased with its host range from 3% for the species feeding on a single plant family to 92% for the species with host range >10 plant families.4. The assemblage on P. aduncum was dominated by a single species {Herpeto-gramma sp. near licarsisalis, Crambidae), which represented 48% of individuals, and also had a high proportion (iA%) of rare species, collected as single individuals. This community structure was indistinguishable from that of a typical native host. In contrast, the P. umbellatum assemblage was unusual as no species represented >10% of individuals.5. The aggressive invasion by P. aduncum of early successional vegetation is not explained by a competitive advantage due to low herbivore load, as the abundance of caterpillars feeding on it was comparable to that of native pioneer plants.6. The caterpillar assemblage on P. aduncum demonstrated that an assemblage indistinguishable from native assemblages in density, species richness, and dominance structure (but not in host specificity) can originate from the existing species pool in lowland rainforests on a recently established tree species in <50 years.