Morphological variation in the polyps of the scleractinian coral Favia speciosa (Dana) around Singapore

A photographic technique was used to examine morphological differences in the living polyps of Favia speciosa sampled from three sites around Singapore. Eight characters were measured, seven of which differed significantly between the three study sites. Sedimentation rates and character size were much higher at the site closest to the mainland than at the two sites further from shore. Land reclamation and dredging contribute to high sediment rates in Singapore waters; these rates decrease with increasing distance from shore. Large polyps close to the main island of Singapore are possibly a plastic, or selected for, response to high levels of sediment.     

Phenotypic plasticity and the possible role of genetic assimilation: Hypoxia-induced trade-offs in the morphological traits of an African cichlid

In this study we investigate the possible role of phenotypic plasticity and genetic assimilation in the process of adaptation and evolutionary change in the cichlid Pseudocrenilabrus multicolor victoriae . In the field we compared a population of a stable hypoxic habitat with one of a stable well-oxygenated habitat. In the laboratory, we compared individuals from the same mother raised under hypoxic or well-oxygenated conditions to examine phenotypic plasticity. Morphological parameters of three categories were measured: (a) the gill apparatus, (b) the surrounding structural elements, and (c) the outer shape of the fish. Swamp-dwelling fish had a 29% greater total gill surface area than fish from the well-oxygenated habitat due to their larger gill filament length and greater lamellar area. In the plasticity experiment, total gill surface area was 18% greater in the hypoxia group due to a larger number of longer filaments. Surrounding elements and outer shape also differed between the field populations and between fish grown under hypoxic and well-oxygenated conditions, but there was disparity between the field results and the plasticity experiment. The disparity between field and experimental fish may be due to: (a) differences in selection pressures between populations, (b) different constraints for genetic and plasticity changes, or (c) selection against plastic responses to hypoxia. Our results suggest that both (a) and (c) are involved.     

Microgeographic variation in shell characters of Littorina saxatilis Olivi—a question mainly of size?

The question of whether there are shape differences between populations of Littorina saxatilis living in different environments is examined by multivariate analyses of 13 morphological characters. Principal component analysis reveals that morphologic differences between populations from habitats with contrasting degrees of wave exposure are mainly due to a general size factor, including shell thickness. Utilizing the group structure among the snails, canonical variate analysis discloses that the main character excluding size that influences subpopulation differentiation is pointedness.     

黄土高原油松和辽东栎林下植物β多样性差异及影响因素

β多样性是生态学研究的热点论题,相同的β多样性格局可能由不同的生态过程所决定.该文通过构建零假说模型和典范变异分解的方法,比较了黄土高原油松人工林(Form.Pinus tabulaeformis)和辽东栎天然林(Form.Quercus wutaishanica)林下植物群落β多样性,确定了环境过滤和扩散限制在β多样...     

Comparative growth in the postnatal skull of the extant North American turtle Pseudemys texana (Testudinoidea: Emydidae)

Bever, G.S. 2007. Comparative growth in the postnatal skull of the extant North American turtle Pseudemys texana (Testudinoidea: Emydidae). —Acta Zoologica (Stockholm) 88 : 000–000 Postnatal growth is one of the many aspects of developmental morphology that remains distinctly understudied in reptiles. Variation and ontogenetic scaling within the skull of the extant emydid turtle, Pseudemys texana is described based on 25 continuous characters. Results indicate that skull shape in this species changes little during postnatal growth relative to the only cryptodire taxa for which comparable datasets are available (Apalone ferox and Sternotherus odoratus). This relative lack of change results in the paedomorphic retention of a largely juvenile appearance in the adult form of P. texana. The skulls of males and females, despite the presence of distinct sexual dimorphism in size, grow with similar scaling patterns, and the few observed differences appear to reflect alteration of the male growth trajectory. Comparisons with A. ferox and S. odoratus reveal a number of similarities and differences that are here interpreted within a phylogenetic context. These preliminary hypotheses constitute predictive statements that phylogenetically bracket the majority of extant cryptodire species and provide baseline comparative data that are necessary for the future recognition of apomorphic transformations. Plasticity of ontogenetic scaling as a response to the homeostatic needs and behaviour of individuals commonly is evoked as a limitation of ontogenetic scaling as a means to inform phylogenetic studies. These evocations are largely unfounded considering that variability itself can evolve and thus be phylogenetically informative.     

Vivid molecular divergence over volcanic remnants: the phylogeography of Megadromus guerinii on Banks Peninsula,New Zealand

Megadromus guerinii, an endemic carabid beetle (Carabidae), is the most common carabid throughout its restricted range on Banks Peninsula, a formation of extinct volcanoes in Canterbury, New Zealand. This study characterises the small-scale phylogeographic patterns of M. guerinii across the formerly volcanically active Banks Peninsula using mitochondrial and ribosomal genes. Between the eastern and western areas of the peninsula, the mitochondrial, but not nuclear, DNA has a well-defined geographic distribution. Specifically, mitochondrial cytochrome c oxidase subunit I (CO1) identifies two distinct groups (> 6% divergence between eastern and western beetles) while ribosomal genes show no discernible pattern. Whether such a pattern represents male-biased dispersal, Wolbachia infection, a recent range expansion of a divergent lineage, or a deeper historic separation is explored. There is potential that male-biased dispersal could have occurred. Wolbachia infection was not detected. We conclude that historical processes have likely separated taxa in the eastern and western peninsula.     

Riffles as barriers to interpool movement by three cyprinids (Notropis boops,Campostoma anomalum and Cyprinella venusta)

1. The effects of riffles as barriers to movement of stream fish was investigated in a set of eight large outdoor artificial streams. Pools were 183 cm in diameter and 45 cm deep; riffles were 183 cm long and 43 cm wide. Rates of movement of three species of minnows (Cyprinidae) (Campostoma anomalum, Cyprinella venusta and Notropis boops) among pools were measured at four riffle current velocities (0, 15, 30 and 45 cm s^–1), three thalweg depths (10, 50 and 100 mm), two riffle lengths (183 and 549 cm), and with and without the threat of predation. Visual observation and video cameras were used to quantify movement rate. 2. Mean movement rate (percentage of fish crossing a riffle each 30 min) was 18.1% at 0 cm s^–1 and only 1.8 at 45 cm s^–1. Movement rate was 7.2% with no predators present and 20.2% with caged predators in pools. Notropis boops had a lower rate of movement than C. venusta or C. anomalum across all trials. The mean group size (number of individuals crossing a riffle together) was 1.2 fish overall, indicating most movement was by individuals and not groups. Group size was significantly greater only with shallow riffles or under the threat of predation. 3. Overall biotic and abiotic factors in these artificial streams do influence movement rates and may affect movement among pools in natural streams.     

Ecology of a diplozoon parasite on the gills of the African cyprinid Barbus neumayeri

In oxygen‐deficient waters, the difficulties of oxygen uptake in gill parasites and their fish hosts may influence host and parasite densities, site selection by the parasite, and effects of the parasite on host condition. This study quantified the prevalence and intensity of the gill monogenean Neodiplozoon polycotyleus in the African cyprinid fish Barbus neumayeri from an intermittent forest stream in western Uganda. Oxygen levels were low in the stream over the 12‐month study, averaging only 2.5 mg litre^?1 (monthly range = 1.2–4.3 mg litre^?1). However, parasite prevalence was high (47.2%), suggesting high tolerance to low oxygen in N. polycotyleus. The prevalence of parasites varied with host body size, with the highest frequency of occurrence in the middle size classes. Prevalence also varied over the year; seasonal peaks of rainfall coincided with a lower frequency of N. polycotyleus. The significantly nonrandom frequency distribution of parasites among hosts suggests regulation of parasite numbers. Of the hosts infected, 37.1% harboured one N. polycotyleus parasite, and 62.9% harboured two parasites. No fish were infected with more than two diplozoons. There was evidence for strong site specificity by N. polycotyleus within hosts; 77.7% of the parasites were located on the filaments of the second gill arch, which may relate to increased oxygen availability. In addition, only one of the 178 infected fish had more than one parasite on one side of the branchial basket. Although N. polycotyleus is undoubtedly parasitic, we found no evidence of a negative parasitic effect on the condition or reproductive status of B. neumayeri.