Evolutionary divergence in common marine ectoparasites Gnathia spp. (Isopoda: Gnathiidae) on the Great Barrier Reef: phylogeography, morphology, and behaviour

The blood‐feeding juvenile stages of gnathiid isopods are important ectoparasites of marine fishes on the Great Barrier Reef (GBR), and are a major component of the diet of cleaner fishes. We report here that these gnathiids have undergone evolutionary diversification, both geographically and temporally (into diurnally and nocturnally active taxa), which has been accompanied by changes in their morphology and behaviour. To perform this analysis, we sequenced a portion of the nuclear ribosomal ITS2 for 47 gnathiids collected from 29 host fishes of 11 species at three locales spanning 2000 km on the GBR. Maximum parsimony and Bayesian phylogenetic analyses both revealed four major clades. There was some degree of geographical structuring in these clades, but there was no evidence supporting host fish specialization, as gnathiids collected from the skin of different teleost taxa did not resolve into distinct clades. The topology of the phylogeny also implied some structuring that was dependent upon collection time (day or night), so we investigated whether there were also behavioural and morphological differences between taxa active at these different times. Nocturnal gnathiids had significantly longer antennules and larger eyes than diurnal gnathiids – two traits presumably adaptive for nocturnal activity. Behavioural tests showed that both nocturnal and diurnal gnathiids use olfaction and vision while foraging, but that nocturnal gnathiids used olfaction more often in dark conditions, and that they were able to perceive movement under extremely low levels of light. Diurnal gnathiids used vision more effectively when there was some ambient light. Our results thus suggest that both phenotypic and genotypic divergence in gnathiids may be influenced by natural selection acting on ecological traits, such as predator avoidance and host detection. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94 , 569–587.     

Climate-related differences in the dominance of submerged macrophytes in shallow lakes

It has been suggested that shallow lakes in warm climates have a higher probability of being turbid, rather than macrophyte dominated, compared with lakes in cooler climates, but little field evidence exists to evaluate this hypothesis. We analyzed data from 782 lake years in different climate zones in North America, South America, and Europe. We tested if systematic differences exist in the relationship between the abundance of submerged macrophytes and environmental factors such as lake depth and nutrient levels. In the pooled dataset the proportion of lakes with substantial submerged macrophyte coverage (> 30% of the lake area) decreased in a sigmoidal way with increasing total phosphorus (TP) concentration, falling most steeply between 0.05 and 0.2 mg L⁻¹. Substantial submerged macrophyte coverage was also rare in lakes with total nitrogen (TN) concentrations above 1–2 mg L⁻¹, except for lakes with very low TP concentrations where macrophytes remain abundant until higher TN concentrations. The deviance reduction of logistic regression models predicting macrophyte coverage from nutrients and water depth was generally low, and notably lowest in tropical and subtropical regions (Brazil, Uruguay, and Florida), suggesting that macrophyte coverage was strongly influenced by other factors. The maximum TP concentration allowing substantial submerged macrophyte coverage was clearly higher in cold regions with more frost days. This is in agreement with other studies which found a large influence of ice cover duration on shallow lakes' ecology through partial fish kills that may improve light conditions for submerged macrophytes by cascading effects on periphyton and phytoplankton. Our findings suggest that, in regions where climatic warming is projected to lead to fewer frost days, macrophyte cover will decrease unless the nutrient levels are lowered.     

Phylloclade anatomy in Phyllanthus section Choretropsis (Phyllanthaceae)

The phylloclade anatomy of nine Brazilian species of the genus Phyllanthus section Choretropsis was studied, and its systematic significance was analysed. The arrangement of epidermal cells varied according to the species, with the guard cells of the stomatal apparatus distributed randomly or with the longitudinal axis parallel to the branch. In both branch types, the stomata were distributed on the phylloclade surface, except in P. gladiatus which showed hypostomatic branches. In most of the species, phylloclades developed a vascular system surrounded by clusters of fibres and cortical parenchyma, which could differentiate into palisade‐like tissue and ground tissue like a true leaf blade. The distribution of the vascular system followed the cylindrical or flattened diameter shape of the branch. In subsection Choretropsis, the cylindrical branches of P. choretroides, contrary to other species, developed a second ring formed by clusters of fibres surrounded by large parenchymal cells. In subsection Applanata, the palisade‐like cells of P. flagelliformis phylloclades acquired an isodiametric shape. The highest level of specialization was observed in P. gladiatus, which developed phylloclades with a dorsiventral structure, a main vein, and small sets of lateral vascular bundles like a typical leaf blade. The tissue arrangement of different species showed a gradual pattern, which was correlated with the different branch morphology and plant architecture. Despite the transitional pattern, it was suggested that some of the phylloclades had an independent origin and convergent evolution in the Choretropsis section. The anatomy of different branch types was shown to be useful, either in isolation or in association with other morphological characters, to delimit the species and to further understand their relationships and phylogeny. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 91–102.     

Dietary Overlap Between Huemul and Livestock in Los Alerces National Park,Argentina

ABSTRACT We evaluated the potential for interspecific competition for forage between huemul (Hippocamelus bisulcus) and livestock in Los Alerces National Park, Argentina. We studied winter diets based on microhistological analysis of fecal samples. Huemul selected herbs and shrubs, sheep showed preference for herbs and grasses, and cattle selected grasses. As predicted for small-bodied species, huemul had a narrower dietary niche than did larger bodied cattle. Competition for forage would be more likely between huemul and sheep than between huemul and cattle. Our results might be helpful to managers in areas where domestic and wild ungulates live in sympatry in order to reduce competition, especially in wintering areas where food is scarce.     

Fossil cocoons associated with a dinosaur egg from Patagonia,Argentina

Abstract: Eight fossil (Cretaceous) insect cocoons were discovered within the infillings of a broken dinosaur egg of a clutch from a Patagonian locality. Cocoons are considered to be in situ based on detailed preservation of thin, delicate walls with surface texture, infillings that are similar to the surrounding rock matrix and the clustered distribution of cocoons in only one egg out of the clutch of five eggs. According to the shape, size, and thin wall with surface texture, the cocoons are interpreted as having been produced by wasps. The wasps may have been attracted to the egg because of the presence of scavenging insects feeding on the decaying organic matter, or they may have been attracted to spiders feeding on the scavenging insects. In either scenario, after attacking the insects or spiders inside the sand infillings of the egg, the wasp larvae produced the cocoons described herein. The presence of wasps, which are at the top of the scavenging food webs, suggests that a complex community of invertebrates would have developed around rotten dinosaur eggs.     

Immune response to nylon filaments in two damselfly species that differ in their resistance to ectoparasitic mites

1. Insects commonly resist parasites using melanotic encapsulation. Many studies measuring immune response use the amount of melanin deposited on an artificial object that has been inserted into the animal as a proxy of the amount of resistance that the host is capable of mounting to natural parasites. 2. The relevance of this methodology to immune response in natural insect populations needs further study. Here, we examined two temperate damselfly species to elucidate the relationships among damselfly size, natural resistance to mites, and the immune response mounted by the same damselflies against nylon filaments. 3. The damselfly species that had high rates of melanotic encapsulation of mites in nature deposited more melanin on the nylon inserts than the species with low rates of natural resistance. 4. In females of this species, those that had resisted mites naturally melanised the nylon filament more aggressively than those that did not resist mites. 5. Our results show some support for the use of nylon filaments to assess natural patterns of immune response in these damselflies, but also suggest that caution should be used in interpreting the responses.