‘House and garden’: larval galleries enhance resource availability for a sedentary caddisfly

1. Sedentary grazers can be numerous in fresh waters, despite the constraints on resource availability and the increased predation risk inherent in this lifestyle. The retreats of sedentary grazers have been assumed to provide protection to the resident (a ‘house’), but also may provide additional fertilised food for the grazer (i.e. a ‘garden’). If retreats function as a garden, then they should (i) contain a higher quality and/or quantity of food than the alternative food source. Furthermore, the proportion of retreat‐derived carbon and nitrogen assimilated by the resident should be (ii) related to overall resource availability (more when resources are limited) or (iii) perhaps also to larval density. Alternatively, if retreats provide a less risky food source, then (iv) assimilation of material from the retreat is likely to be greater under conditions in which the risk of emerging from the retreat is high. 2. We tested these four hypotheses for the common and widespread gallery‐building grazing caddisfly Tinodes waeneri. Resource availability, larval density and biomass, and exposure were measured for populations from six lakes of differing productivity in August, October and January. 3. Galleries always contained more algal food than the surrounding epilithon, suggesting that gardening is effective. Furthermore, gallery chlorophyll a content in August, and the disparity in food quality (assessed from the C : N ratio) between gallery and epilithon (quality higher in the former) in October were positively related to the proportion of larval biomass that was derived from the gallery. Larval density and wave exposure parameters were not related to larval assimilation of gallery material. 4. Galleries that are fertilised by the occupant provide more, and sometimes also better quality, food (in terms of the C : N ratio) than is otherwise available. Thus, the gallery plays a substantial role in larval nutrition, and this role is greater at key times of food shortage.     

Encephalitozoon cuniculi Isolated from the Urine of an AIDS Patient, which Differs from Canine and Murine Isolates

ABSTRACT. A species of Encephalitozoon has been isolated from the urine of a patient with the acquired immunodeficiency syndrome and maintained in vitro in Madin Darby Canine Kidney cells. When examined by random amplified polymoprhic DNA polymerase chain reaction the new isolate was found to differ from E. hellem and to have amplified products in common with murine and canine E. cuniculi . However, it more closely resembled the canine than the murine isolate. Sodium dodecylsulphate polyacrylamide gel electrophoresis differentiated between all three isolates of E. cuniculi , with a band at 42–45 kDa present in the murine isolate only, bands at 52 kDa present in the canine and human isolates but not the murine, and a single band at 60 kDa (murine) and 65 kDa (canine) replaced by two bands at 55 and 70 kDa in the human isolate. The 55 kDa and 70 kDa antigens were also revealed as characteristic bands of the human isolate by Western blotting. The study has thus revealed that the species Encephalitozoon cuniculi is not a homogeneous entity.     

Spatial and genetic investigation of aggregation in Ischnochiton (Polyplacophora; Neoloricata; Ischnochitonina; Ischnochitonidae; Ischnochitoninae) species with different larval development

Many species are aggregated at some spatial scale but for some species, due to habitat or behaviour, aggregation can be difficult to assess quantitatively. Here, aggregation of chiton species (Polyplacophora; Neoloricata; Ischnochitonina; Ischnochitonidae; Ischnochitoninae; Ischnochiton) living under boulders in intertidal boulder fields was investigated at several relatively small spatial scales. Closely related species were found to be aggregated at the level of individual boulders, but evidence for grouping at the larger scale of patches of boulders varied. When organisms are mobile, dispersal can have an important influence on spatial patterns. Some organisms, such as marine invertebrates, have a highly dispersive larval phase that can influence spatial patterns of adults, particularly where the adult is sessile or relatively sedentary. Aggregation was compared in two species to test whether different modes of larval development influence spatial pattern. There was some evidence that species with a planktonic larva were even more aggregated than expected, in contrast to predictions based on this mode of development. Both types of larval development (planktonic and non‐planktonic) produce larvae with short development times in these species, so one possible explanation for the grouping habit of these chitons is that they do not disperse, at all, from their natal boulder. The complexity of the boulder field habitat and the cryptic behaviour of these chitons may also contribute to a lack of dispersal. A simple application of a genetic method indicated, however, that philopatry at this scale is unlikely.     

Ontogenetic variation in density‐dependent growth of brown trout through habitat competition

1. Density‐dependent growth has been widely reported in freshwater fishes, but the ontogenetic evolution of competition and its subsequent effects on growth through a life span remains unclear. 2. Patterns of competition can be described by integrating population abundance data with habitat‐modelling results. Weighted usable area (WUA; m² WUA ha^?1) curves are obtained for each flow value and are then coupled with demographic data to obtain the occupancy rates (trout m^?2 WUA, the density of a given age class related to its suitable habitat) of the WUA for every age class, year and site. 3. We examined a long‐term data series searching for temporal variation in the influence of habitat occupancy rate on the growth of brown trout Salmo trutta. We tested whether (i) mean cohort mass (mean mass of the cohort during the first 3 years of life) is affected by the occupancy rate experienced across a life span; and (ii) the occupancy rate experienced at different ages influenced mean body size. 4. We observed a consistent negative power relationship between average cohort mass and mean occupancy rate through a life span, indicating that stronger cohorts were related to a reduced growth, with likely consequences for individual fitness. 5. The effects of occupancy rate on size‐at‐age were mainly detected in the size attained at the second year of life, but they were because of the competition at different times. Thus, the level of competition varied through ontogeny, in some of the rivers affecting growth since the first year of life, whereas in most of the rivers the main effects on body size resulted from the competition during the second year of life. 6. Occupancy rate appears more appropriate than density for assessing the occurrence of habitat competition in freshwater fishes, since it encompasses the differences in quantity and quality of suitable habitat for each age class. 7. Our study highlights the importance of density‐dependent growth as a key process in the dynamics of brown trout populations, its temporal variation depending on the temporal changes of density and the variation of competition associated with the habitat capacity for each life stage.     

Microsatellite markers for evolutionary studies in the sexually deceptive orchid genus Chiloglottis

The orchids in the genus Chiloglottis are pollinated exclusively by sexual deception. We describe 20 variable microsatellite loci that will facilitate the study of the evolution and ecology of this specialized pollination system. Two loci were isolated from Chiloglottis trilabra, with the rest derived from Chiloglottis valida. All loci were polymorphic in C. valida (H_E 0.07–0.87). Most loci amplified, and were variable within close relatives of C. valida, and a number amplified more broadly, including outside the genus.