Assortative mating across a hybrid zone in Chorthippus parallelus (Orthoptera: Acrididae)

Two subspecies of the grasshopper Chorthippus parallelus meet and form a hybrid zone in the Pyrenees. Both strong hybrid dysfunction and a behavioural difference occur, which would seem to make the zone a suitable candidate for speciation by reinforcement. One of the classic ways of looking for this is to test for increased levels of assortative mating between populations from close to the region of contact. Here we show that, with virgin insects, such assortment decreases as one approaches the centre of the zone in C. parallelus. The pattern is different upon remating, with non-virgins showing a pattern more like that predicted by reinforcement. Overall there is little evidence for reinforcement. We argue that other tests of the model may be more appropriate for stable hybrid zones.     

Climate and vegetation in China II. Distribution of main vegetation types and thermal climate

The authors examined relationships between Kira's warmth index (WI) and four other important thermal indices: the sums of daily mean temperatures above 5°C and 10°C, Thornthwaite's potential evapotranspiration (PE) and Holdridge's annual biotemperature. The thermal records of 671 meteorological stations evenly located all over China were used to make these comparisons. Close correlations were found within the four relationships, and accordingly WI was used to analyse the thermal distributions of the main vegetation types. Vegetation types around the 671 stations were read from a vegetation map with a scale of 1/4000000. Vegetation types at 269 stations corresponded to the natural or seminatural vegetation, and 29 vegetation types were distinguished by arranging the 269 data into the same or similar types. The geographical distribution of these 29 types and the corresponding main climatic features were described. The relations between WI and distribution of these vegetation types were discussed in detail. As a result, WI values (°C month) corresponding to the vegetation zones could be summarized as follows: (1) arctic or alpine vegetation zone: 0–15; (2) boreal or subalpine vegetation zone: 15-(50–55); (3) cool-temperate vegetation zone: (50–55)–(80–90); (4) warm-temperate vegetation zone: (80–90)–(170–180). These values almost coincided with Kira's values. Chinese postgraduate student in Japan sent by the Chinese Government.     

Conserved organization of an avian histone gene cluster with inverted duplications of H3 and H4 genes

Summary The organization of histone gene clusters of the duckCairina moschata was studied in the DNA inserts of two recombinant phage that overlap and feature identical histone gene arrangements but differ in sequence details and in the extent of repetition of an AT-rich motif in one of the nontranscribed spacer regions. These few but substantial differences between otherwise nearly identical histone gene groups suggest that we have independently isolated alleles of the same site of the duck genome or that this gene arrangement occurs (with slight variations) more than once per haploid genome. Within the histone gene cluster described, H3 and H4 genes are duplicated (with inverted orientation), whereas one H1 gene is flanked by single H2A and H2B genes. The arrangement of duck histone genes described here is identical to a subsection of the chicken genome but differs from any other published histone gene cluster.     

Genetic structure of Glycine canescens,a perennial relative of soybean

Summary Allozyme variation as detected by starch gel electrophoresis was used to assess the extent and spatial organization of genetic variation across the entire range of Glycine canescens sensu lato. Eleven enzyme systems were assayed in 116 accessions of this taxon and 102 alleles were detected at a total of 31 loci. Eighty-one percent of loci were polymorphic. Most of this variation occurred between and very little within accessions. Three major groupings were detected. These groupings (groups 1, 2, and 3) also differed with respect to mean seed size and their geographic distribution. A further ten accessions stood out from these distinct groups. These accessions were most closely related to group 3 but were variable among themselves. In general, they were collected from highly dissected terrain, often in the remote interior of the continent. A final group of 18 problematic accessions (group X), originally tentatively identified as G. canescens on morphological grounds, was shown to be isozymically distinct from this species and was reclassified as one form of the polytypic species G. clandestina.     

Spatial and temporal distributions of salmonids in two ponds in Newfoundland, Canada

Spatial and temporal distributions of salmonids were examined in Junction Pond, Northeast River, Placentia and Conne Pond, Conne River, Newfoundland using Lundgren multiple-mesh experimental gillnets. Both ponds contain populations of Atlantic salmon and brook trout with Junction Pond also possessing brown trout and resident Arctic charr. For salmon parr there was a significant month effect in distribution of catch rates in both ponds, and in Junction Pond, there was a significant diel effect. There was also significant variation in catch rates by lentic zone. For brook trout, there was a significant lentic zone × month interaction in Junction Pond; in Conne Pond, the main effects lentic zone and month were significant. Highest benthic catch rates of Atlantic salmon parr occurred in the littoral zone of both ponds. Most captures of brook trout also occurred benthically in both ponds; similar to salmon parr, littoral zone catch rates were higher than those of the deeper benthic area in Conne Pond but the reverse was true for Junction Pond. For both salmon parr and brook trout, the deeper benthic area and the pelagic area were relatively important rearing habitats in each pond. The distribution of catches for brown trout (few in number relative to the other species) in Junction Pond was similar to that of brook trout while Arctic charr were found mainly pelagically. Within the benthic area, most Arctic charr were caught at depths beyond the littoral zone. There was a tendency for Altantic salmon parr and brook trout found in the deeper benthic area and the pelagic area to be significantly larger and older than those in littoral zone in each pond. Sizes of Arctic charr did not differ significantly among lentic zones.     

LACK OF CALLING SONG DISPLACEMENT BETWEEN TWO CLOSELY RELATED GROUND CRICKETS

Thorough examinations of purported cases of reproductive character displacement are critical for reaching an understanding of the role of reinforcement in the evolution of reproductive barriers between closely related species. In this paper, we report the results of an extensive investigation of male calling song variation in the ground crickets, Allonemobius fasciatus and A. socius. Contrary to the results of an earlier study, we uncovered little evidence of displacement of songs in areas of overlap. We discuss explanations for the lack of displacement as well as for the discrepancies between the results of the current study and those of the earlier study.     

LIFE-HISTORY ADAPTATION AND REPRODUCTIVE ISOLATION IN A GRASSHOPPER HYBRID ZONE

Patterns of life-history adaptation and reproductive isolation were investigated in the acridid grasshoppers Melanoplus sanguinipes and M. devastator, which hybridize along an altitudinal gradient in the Sierra Nevada of California. Melanoplus sanguinipes females crossed with M. devastator males produced eggs that were approximately half as viable as eggs from other crosses. Diminished viability was not attributable either to infection by Wolbachia pipientis or to failure of sperm transfer. When offered an opportunity to choose a mate, females from all populations discriminated against males of the other species, whereas in no-choice tests measuring copulation duration only females from the tails of the clines showed preferences. Melanoplus sanguinipes, found at high elevations where the growing season is short, exhibited faster egg hatch, faster larval development, smaller adult body sizes, and smaller clutch sizes than M. devastator. Melanoplus devastator, from California's Central Valley, endured a hot and dry summer in a reproductive diapause that was absent in M. sanguinipes. Clines in reproductive diapause and clutch size coincided with the region of reproductive incompatibility. Development time, body size, and hatch time also changed across the hybrid zone, but the regions of largest transitions in these traits were either difficult to locate using the limited populations studied here or were not coincident with the zone's center. A method is described for combining ecological and phylogenetic analyses to address the unknown issue of whether life-history divergence has conributed to reproductive isolation in this system.     

A new species of Macrothrix (Anomopoda: Macrothricidae) from Central Mexico

Macrothrix mexicanus sp. nov. is described from central México, a transition zone between the nearctic and neotropics. All localities where it was found are over 1800 meters above sea level. It shows many resemblances with M. laticornis, M. camjatae and M. rosea but is characterized by a persistent dorsal tooth on the valve keel, a spinous papilla on the basipodite of the antenna, the second thoracic limb with a long conical sensillum between scraper 1 and the gnathobase, the endopod of trunk limb IV having two setae; the postabdomen with the dorsal margin bilobed, and the distal segment of the seta natatoria which is unusually long.Abbreviations used on figures EN Endopodite - EP Epipodite - EX Exopodite - IDL Inner distal lobe - ODL Outer distal lobe - GT Gnatobase - E1 Endite 1 - E2 Endite 2 - E3 Endite 3     

Effect of riparian land use on contributions of terrestrial invertebrates to streams

Since terrestrial invertebrates are often consumed by stream fishes, land-use practices that influence the input of terrestrial invertebrates to streams are predicted to have consequences for fish production. We studied the effect of riparian land-use regime on terrestrial invertebrate inputs by estimating the biomass, abundance and taxonomic richness of terrestrial invertebrate drift from 15 streams draining catchments with three different riparian land-use regimes and vegetation types: intensive grazing — exotic pasture grasses (4 streams), extensive grazing — native tussock grasses (6 streams), reserve — native forest (5 streams). Terrestrial invertebrate drift was sampled from replicated stream reaches enclosed by two 1 mm mesh drift nets that spanned the entire channel. The mean biomass of terrestrial invertebrates that entered tussock grassland (12 mg ash-free dry mass m^–2 d^–1) and forest streams (6 mg AFDM m^–2 d^–1) was not significantly different (p > 0.05). However, biomass estimated for tussock grassland and forest streams was significantly higher than biomass that entered pasture streams (1 mg AFDM m^–2 d^–1). Mean abundance and richness of drifting terrestrial invertebrates was not significantly different among land-use types. Winged insects contributed more biomass than wingless invertebrates to both pasture and tussock grassland streams. Winged and wingless invertebrates contributed equally to biomass entering forest streams. Land use was a useful variable explaining landscape-level patterns of terrestrial invertebrate input for New Zealand streams. Evidence from this study suggests that riparian land-use regime will have important influences on the availability of terrestrial invertebrates to stream fishes.     

Altitudinal zonation of montane Quercus forests along two transects in Chirripó National Park,Costa Rica

Abiotic and vegetation data were collected along two altitudinal transects through mature montane Quercus forests on the Pacific and Atlantic slopes of Costa Rica's Chirripó Massif. Between 2000 and 3200 m asl twenty-four 0.05 ha forest plots were selected at altitudinal intervals of 100 m, and eight soil profiles were described at intervals of 200 m. A TWINSPAN classification aided in the determination of eight zonal forest communities on the basis of their floristic composition. They are grouped in two sets of four: (i) the palm-rich lauraceous-fagaceous Lower Montane Mollinedia-Quercus Forests (2000–2600 m asl) and (ii) the bamboo-rich myrsinaceous-fagaceous Upper Montane Schefflera-Quercus Forests (2500–3200 m asl), respectively. Vegetation changes seem correlated with two major climatic gradients: (i) a temperature gradient (altitude), and (ii) a moisture gradient (wet Atlantic vs. moist Pacific slope). Most soils are Andepts, and residual, colluvial or derived from volcanic material. Humus layers are thicker on the wetter Atlantic slope. A total of 431 vascular plant species consisted of 86 pteridophytes, 1 gymnosperm, 296 dicots and 48 monocots. Species richness, canopy height and stem diameter decrease with increasing altitude, while the canopy surface becomes more flattend. A comparison with other studies shows that Chirripó's montane Quercus forests fit within the environmental ranges known from altitudinal zonations elsewhere in the Tropics.Abbreviations asl above sea level - dbh diameter at breast height - LM Lower Montane - Mt. Mountain - TWINSPAN two way indicator species analysis - UM Upper Montane - VU code referring to soil profiles as presented in Van Uffelen (1991) This paper is dedicated to the memory of Alwyn H. Gentry, an outstanding and inspiring tropical botanist who tragically died in a plane crash in the mountains of Ecuador on August 3 1993, when surveying possible boundaries for a new tropical cloud forest reserve.