Seasonal differences in routine oxygen consumption rates of the bonnethead shark

Routine oxygen consumption rates of bonnethead sharks, Sphyrna tiburo , increased from 141·3±29·7 mg O₂ kg⁻¹ h⁻¹ during autumn to 218·6±64·2 mg O₂ kg⁻¹ h⁻¹ during spring, and 329·7±38·3 mg O₂ kg⁻¹ h⁻¹ during summer. The rate of routine oxygen consumption increased over the entire seasonal temperature range (20–30° C) at a Q ₁₀=2·34.     

Directional mitochondrial introgression and character displacement due to reproductive interference in two closely related Pterostichus ground beetle species

Reproductive interference due to interspecific hybridization can lead to character displacement among related species with overlapping ranges. However, no studies have examined which reproductive traits are most important in reducing reproductive interference. We conducted molecular analyses of two nuclear genes (28S and Wingless) and a mitochondrial gene (COI) from two closely related ground beetle species, Pterostichus thunbergi and Pterostichus habui (Coleoptera: Carabidae), with overlapping distributions. In addition, we examined four reproductive traits (body size, organ morphologies of intromittent and non‐intromittent male genital organs, and female reproductive period) in sympatric and allopatric habitats. We compared male genital morphology using geometric morphometric analysis. The species determined by morphology were classified into separate groups based on the phylogenetic tree constructed by the nuclear gene (Wingless). However, according to the mitochondrial genes examined, P. thunbergi was not monophyletic, whereas at the sympatric sites, these species formed a monophyletic clade. This incongruence suggests that interspecific hybridization and subsequent mitochondrial introgression from P. habui to P. thunbergi have occurred. Concerning genital morphology, both of the intromittent and nonintromittent organs of P. thunbergi differed more from P. habui at the sympatric sites than between allopatric sites, suggesting reproductive character displacement. Pterostichus thunbergi, which likely arrived in P. habui habitat in small numbers, would have experienced stronger selection pressures than P. habui.     

Respiration rates of two species of Gnathostomulids

Summary Respiration rates for two species of Gnathostomulida from poorly oxygenated subtidal sands of Bermuda were measured using Cartesian diver respirometers.ForHaplognathia cf.ruberrima a respiration-body weight regression gaveR=0.790·W ^0,649 (in l·10^-3O₂/h and g wet weight). Respiration rates for adult animals ofGnathostomula sp. of a mean weight of 1.3 g ranged between 0.25 and 0.63 l·10^-3 O₂/h. These rates are low when compared with literature data on meiobenthic species from a wider habitat range but similar to respiration rates of marine and limnic nematodes living in sediments with strongly reducing capacity.     

北京2种阔叶树不同高度枝干的呼吸速率及其对温度的敏感性

该研究采用红外气体分析法(IRGA)于2013年3-12月原位测定了北京市东升八家郊野公园中2个主要阔叶树种(槐(Sophora japonica)、旱柳(Salix matsudana)) 3个高度上的枝干呼吸(R_w)日进程, 旨在量化R_w的种间差异, 探索种内R_w及其温度敏感系数(Q₁₀)的时间动态和垂直分布格局。研究结果显示: (1) R_w在不同树种之间差异明显, 相同月份(4月份除外)槐R_w是旱柳的1.12 (7月)-1.79倍(5月)。两树种枝干表面CO₂通量速率均表现出明显的单峰型季节变化, 峰值分别出现在7月((5.13 ± 0.24) μmol·m^-2·s^-1)和8月((3.85 ± 0.17) μmol·m^-2·s^-1)。同一树种在生长月份内的平均呼吸水平显著高于非生长季, 但其Q₁₀值季节变化趋势与之相反。(2) R_W随测量高度的增加而升高, 并在3个高度上表现出不同的日变化规律: 其中, 树干基部及胸高位置为单峰格局, 而一级分枝处的呼吸速率在一天内存在两个峰值, 中间出现短暂的“午休”现象。温度是造成一天内呼吸变化的主要原因。此外, 顶部R_w及其对温度的敏感程度明显高于基部。温度本身和Q₁₀值差异可在一定程度上解释R_W的垂直梯度变化。(3)在生长月份, 单位体积木质组织的日累积呼吸速率(mmol·m^-3·d^-1)与受测部位直径倒数(D^-1)呈极显著正相关关系。单位面积(μmol·m^-2·s^-1)可准确表达两树种在生长期间的R_W水平, 能合理有效地比较不同个体的呼吸差异及同一个体的时空变异。这些结果表明, 采用局部通量法上推至树木整体呼吸时, 应全面考虑R_w的时、空变异规律, 并选择恰当的表达单位, 以减小估测误差。     

Exploring species limits in two closely related Chinese oaks

BACKGROUND: The species status of two closely related Chinese oaks, Quercus liaotungensis and Q. mongolica, has been called into question. The objective of this study was to investigate the species status and to estimate the degree of introgression between the two taxa using different approaches. METHODOLOGY/PRINCIPAL FINDINGS: Using SSR (simple sequence repeat) and AFLP (amplified fragment length polymorphism) markers, we found that interspecific genetic differentiation is significant and higher than the differentiation among populations within taxa. Bayesian clusters, principal coordinate analysis and population genetic distance trees all classified the oaks into two main groups consistent with the morphological differentiation of the two taxa rather than with geographic locations using both types of markers. Nevertheless, a few individuals in Northeast China and many individuals in North China have hybrid ancestry according to Bayesian assignment. One SSR locus and five AFLPs are significant outliers against neutral expectations in the interspecific FST simulation analysis, suggesting a role for divergent selection in differentiating species. MAIN CONCLUSIONS/SIGNIFICANCE: All results based on SSRS and AFLPS reached the same conclusion: Q. liaotungensis and Q. mongolica maintain distinct gene pools in most areas of sympatry. They should therefore be considered as discrete taxonomic units. Yet, the degree of introgression varies between the two species in different contact zones, which might be caused by different population history or by local environmental factors.     

The influence of herbivory and weather on the vital rates of two closely related cactus species

Herbivory has long been recognized as a significant driver of plant population dynamics, yet its effects along environmental gradients are unclear. Understanding how weather modulates plant–insect interactions can be particularly important for predicting the consequences of exotic insect invasions, and an explicit consideration of weather may help explain why the impact can vary greatly across space and time. We surveyed two native prickly pear cactus species (genus Opuntia) in the Florida panhandle, USA, and their specialist insect herbivores (the invasive South American cactus moth, Cactoblastis cactorum, and three native insect species) for five years across six sites. We used generalized linear mixed models to assess the impact of herbivory and weather on plant relative growth rate (RGR) and sexual reproduction, and we used Fisher's exact test to estimate the impact of herbivory on survival. Weather variables (precipitation and temperature) were consistently significant predictors of vital rate variation for both cactus species, in contrast to the limited and varied impacts of insect herbivory. Weather only significantly influenced the impact of herbivory on Opuntia humifusa fruit production. The relationships of RGR and fruit production with precipitation suggest that precipitation serves as a cue in determining the trade‐off in the allocation of resources to growth or fruit production. The presence of the native bug explained vital rate variation for both cactus species, whereas the invasive moth explained variation only for O. stricta. Despite the inconsistent effect of herbivory across vital rates and cactus species, almost half of O. stricta plants declined in size, and the invasive insect negatively affected RGR and fruit production. Given that fruit production was strongly size‐dependent, this suggests that O. stricta populations at the locations surveyed are transitioning to a size distribution of predominantly smaller sizes and with reduced sexual reproduction potential.     

Distinct male reproductive strategies in two closely related oak species

Reproductive strategies of closely related species distributed along successional gradients should differ as a consequence of the trade‐off between competition and colonization abilities. We compared male reproductive strategies of Quercus robur and Q. petraea, two partly interfertile European oak species with different successional status. In the studied even‐aged stand, trees of the late‐successional species (Q. petraea) grew faster and suffered less from intertree competition than trees of the early‐successional species (Q. robur). A large‐scale paternity study and a spatially explicit individual‐based mating model were used to estimate parameters of pollen production and dispersal as well as sexual barriers between species. Male fecundity was found to be dependent both on a tree's circumference and on its environment, particularly so for Q. petraea. Pollen dispersal was greater and more isotropic in Q. robur than in Q. petraea. Premating barriers to hybridization were strong in both species, but more so in Q. petraea than in Q. robur. Hence, predictions based on the competition–colonization trade‐off are well supported, whereas the sexual barriers themselves seem to be shaped by colonization dynamics.     

Seasonal changes in habitat preferences of two closely related millipede species

The habitat preferences of two closely related millipede species, Centrobolus richardii and C. fulgidus, were investigated on three different seral stages of a coastal dune forest successional sere north of Richards Bay, South Africa. Fixed‐width transects were used to survey millipedes in three habitats of different ages. Habitat preference occurred on both inter‐ and intra‐site levels and was influenced by season. A habitat shift was recorded for C. richardii, while C. fulgidus was dormant during the winter months, reflecting two different strategies used by these closely related species to meet their resource requirements. Successional changes previously reported are masked by these differential responses.     

A chromosomal investigation of two closely related species of Spodoptera

This paper reports the first cytogenetic study of the two closely related species of noctuid moths, Spodoptera latifascia and S. descoinsi. Chromosomes were prepared using a spreading technique on warm slides. Both gonads and larval brains, which are innovating in the Lepidoptera, were used. Out of 100 specimens observed, 35 showed mitotic metaphases, which allowed chromosomes to be counted. For both species and F1 hybrids, the diploid chromosome number was 2n = 62. The chromosomes of the two species appeared dot-shaped, more rarely rod-shaped, showing little variation in size or morphology. The preparations from larval brains also suggested the existence of two levels of ploidy (haploidy and diploidy) in some nuclei. This result will need further investigation. For the first time in the Lepidoptera, in situ hybridization with Drosophila rDNA as a probe was carried out on S. latifascia and S. descoinsi. It revealed the presence of nucleolar organizing regions located at the distal part of one chromosome pair. Though no sophisticated characterization of S. latifascia and S. descoinsi was possible, it seemed that there was no major chromosomal difference. No karyotypic element could be identified as being involved in reproductive isolation between the two species.     

Characterization of microsatellite loci in two closely related Lissotriton newt species

We have developed eight di- and tetranucleotide Lissotriton microsatellite markers. Eight loci were polymorphic in the palmate newt Lissotriton helveticus and six were polymorphic in the smooth newt L. vulgaris. Polymorphism detected in 33 and 37 individuals per species ranged from 3 to 15 alleles. These markers are suitable for the investigation of population structure, genetic variation and taxonomic identification in the two focal species, and may also be of use in other Lissotriton–Triturus species.     

Homology of Balbiani Ring DNA in two closely related Chironomus species

Cytogenetic analysis indicates that Balbiani Ring 2 (BR 2) in the two sibling species Chironomus tentans and Chironomus pallidivittatus arises from identifically banded segments in the salivary gland polytene chromosomes, although chromosomal rearrangements have occurred. In situ hybridization of BR 2 RNA to the polytene chromosomes of each individual species, as well as their F1 hybrids, reveals that the repetitious BR 2 DNA in the two species has, within the limits of the technique, retained identity of nucleotide sequences and degree of repetition. The DNA of the naturally expressed BR 1 and BR 3 in both species and that ot the galactose induced BR 6 in C. pallidivittatus did not hybridize with BR 2 RNA, indicating that these BR's are different from BR 2 with regard to sequence content.     

Fecundity in relation to wing-morph of three closely related species of the melanocephalus group of the genus Calathus (Coleoptera: Carabidae)

Summary In two successive years the fecundity of the carabid beetles Calathus (Neocalathus) cinctus, C. (N.) melanocephalus and C. (N.) mollis was studied in relation to wing-morph and temperature. Differences were found between the three species in both egg production and timing and length of the oviposition period. In all species the fecundity of laboratory bred beetles was significantly higher than that of females collected in the field. Long-winged females of both cinctus and melanocephalus had significantly higher egg production than short-winged females, and they also tended to produce eggs over a longer period. In mollis only the fecundity of the long-winged morph was established. The observed lower relative fitness of the short-winged morph in both cinctus and melanocephalus contradicts the supposed increase of the frequency of this morph in ageing, more or less isolated, populations of these species. The loss of long-winged genotypes, resulting from flight activities, is considered the most plausible cause of the increase of short-winged beetles in ageing populations. The higher fecundity of macropterous females makes them especially suited for (re)establishing populations.Communication No. 429 of the Biological Station WijsterPresent address and address for offprint requests: Kortenburg 31, NL-6871 ND Rentum     

Oxygen Consumption and Respiration During and After two Yoga Relaxation Techniques

Cyclic meditation (CM) is a technique which combines ‘stimulating’ and ‘calming’ practices, based on a statement in ancient yoga texts suggesting that such a combination may be especially helpful to reach a state of mental equilibrium. The oxygen consumption, breath rate and breath volume of 50 male volunteers (group mean age±SD, 27±6.3 years) were assessed before, during, and after sessions of CM and sessions of supine rest in the corpse posture (shavasana, SH). The sessions were one day apart and the order was alternated. The oxygen consumption, breath rate and breath volume increased during the ‘stimulating’ practices of CM, returned to the baseline during the ‘calming’ practices, and the oxygen consumption decreased by 19.3 percent below baseline values after CM. During the SH session the oxygen consumption, breath rate and breath volume reduced; however the decrease in oxygen consumption after SH was less than after CM (i.e., 4.8 percent). The results support the idea that a combination of yoga postures with supine rest (in CM) reduces the oxygen consumption more than resting supine alone does.     

A new morphometric model in distinguishing two closely related extinct brachiopod species

Pseudoatrypa (Atrypida, Brachiopoda) are extinct Paleozoic brachiopods that are the closest relatives of the modern brachiopods, rhynchonellids. Two Paleozoic brachiopod species were qualitatively distinguished based on close examination of phenotypic characters and traditional morphometrics. These species were recovered for the first time from the Givetian localities of Traverse Group of Michigan. The efficacy of geometric morphometric analyses in discriminating species has been proven for various organisms, but rarely studies have been performed in distinguishing brachiopod species. The advanced morphometric model developed here using the Procrustes-based landmark method is based on the analysis of valve shape in two extinct brachiopod species: Pseudoatrypa lineata and Pseudoatrypa devoniana. Results from quantitative analyses reinforce the qualitative identifications of the two species. The application of this method on four different orientations (dorsal, ventral, posterior and anterior regions) of the brachiopods permits the two species to be clearly separated, and this study proposes that the model can be effectively used for future identification and distinction of fossil species. Additionally, this study will aid biologists, paleontologists and neontologists in making appropriate advancement in systematic studies and further assist with gauging biodiversity congruously.     

Intraspecific variation in reproductive barriers between two closely related Arabidopsis sister species

Reproductive isolation (RI) is a critical component of speciation and varies strongly in timing and strength among different sister taxa, depending on, for example the geography of speciation and divergence time. However, these factors may also produce variation in timing and strength among populations within species. Here we tested for variation in the expression of RI among replicate population pairs between the sister taxa Arabidopsis lyrata subsp. lyrata and A. arenicola. While the former is predominantly outcrossing, the latter is predominantly selfing. We focused on intrinsic prezygotic and postzygotic RI as both species occur largely in allopatry. We assessed RI by performing within-population crosses and interspecific between-population crosses, and by raising offspring. RI was generally high between all interspecific population pairs, but it varied in timing and strength depending on population history. Prezygotic isolation was strongest between the closest-related population pair, while early postzygotic isolation was high for all other population pairs. Furthermore, the timing and strength of RI depended strongly on cross direction. Our study provides empirical support that reproductive barriers between species are highly variable among population pairs and asymmetric within population pairs, and this variation seems to follow patterns typically described across species pairs.     

Inducible defences in Daphnia: responses to two closely related predator species

The predator-induced responses of two species of Australian Daphnia, with contrasting distributions and life history patterns, to the kairomones of two species of Anisops predators, were measured. Daphnia longicephala produced a large crest and attained a larger size when exposed to both predators. D. carinata sl matured earlier than D. longicephala and did not produce a crest. Surprisingly, kairomones of both predators inhibited the production of ephippia in D. carinata sl. Anisops stali, the larger of the two predator species, induced a significantly larger crest size in D. longicephala, and larger brood size in both species compared with the smaller A. gratus, indicating a quantitative but not qualitative effect of predator species on inducible defences. Received: 18 August 1999 / Accepted: 14 April 2000