Microsatellite loci for Cherrie's tanager (Ramphocelus costaricensis)

Cherrie's tanager (Ramphocelus costaricensis) is a common woodland bird of the Pacific lowlands of Costa Rica. Males and females have sexually dimorphic plumage and are socially monogamous. As part of a study of sexual selection in this species, we characterized six species‐specific polymorphic microsatellite loci and one cross‐species locus that works well in Cherrie's tanager to ascertain parentage.     

Efficient estimation of temperature distribution, heat storage, thermocline migration and vertical eddy conductivities in stratified lakes

1. Factorial designs were used to investigate the spatial and temporal components of temperature sampling error in two medium-sized (maximum fetch = 9 and 11 km; maximum depth = 24 and 70m) Wisconsin lakes (Mendota and Green). Sampling designs were then optimized for estimating temperature distributions, thermocline migration, lake heat content, and vertical eddy conductivities in these and similar stratified lakes. 2. Errors were at a minimum for: (i) isotherms positioned ¹/₃ - ¹/₂ of the way down through the seasonal thermocline; (ii) at lake stations located near the node of the principal internal seiche; (iii) after an extended interval of low windpower. If seven spatially distributed lake stations were sampled n₁, n₂ times during the two low-power intervals bracketing a weather front, and the rime delay between revisits was randomized with respect to the period of the uninodal temperature seiches, the resulting standard error (cm) in ΔZ?₁₇ (depth of 17° isotherm; an unbiased, minimum-variance estimator for main thermocline migration) was (144/n₁+ 144/n₂)^1/2. If n₁=n₂= 2 ‘revisits’, the resulting CV (coefficient of variation) was 5–10% for ΔZ?₁₇ accompanying major individual cold fronts in early summer. 3. When estimating K_z, the vertical eddy conductivity, the most important component of error relates to ΔH_z, the change in heat content below depth z. The error in ΔH_z is minimized in the same manner as for lake-mean isotherm depth. Using the Mendota sampling design described above, the RMS error in ΔH_z decreases from ～90 cal cm^?2 in the upper metalimnion to ～35calcm^?2 near the base of the metalimnion. For seven take stations, and n₁= n₂= 2, K_z can be estimated with a CV ～10% bracketing a single major cold front. The CV decreases approximately as ΔH_z^?1, hence is roughly proportional to Δt^?1 or to (cumuiative windpower)^?1.     

Do agricultural pollutants affect competition between filter‐feeding caddis fly larvae? Results of laboratory microcosm experiments

1. Predictable changes in the composition of macroinvertebrate communities in response to non‐point source pollution are the basis of macroinvertebrate community indices. However, other factors, such as biotic interactions, also affect the composition of macroinvertebrate communities and may complicate the interpretation of such indices by interacting with abiotic stressors. 2. The effect of agricultural pollutants on competition between two filter‐feeding caddisflies, Brachycentrus appalachia and Hydropsyche spp. was studied in the laboratory using recirculating flow tanks. 3. Experiments were conducted at two densities of Hydropsyche: high (300 per tank) and low (80 per tank). Brachycentrus density was kept constant at 40 per tank in all experiments. Experiments assessed the effect of an agricultural pollutant mix (sand, cow‐manure compost mix) and the presence of the competitor on both taxa. 4. The only negative response to pollutants was a larger number of Hydropsyche drifting in high‐density tanks. In fact, at high densities, mortality of Hydropsyche was higher in controls than in tanks receiving pollutants. 5. Hydropsyche and B. appalachia competed for resources and the presence of pollution did not affect the outcome of this competition. The presence of high densities of Hydropsyche resulted in higher drift and lower condition of B. appalachia. At low densities of Hydropsyche, B. appalachia larvae suffered greater mortality and tended to be in poorer condition. Brachycentrus appalachia may be less successful at even moderate densities of Hydropsyche due to competition between these taxa, most likely for prime feeding positions. 6. Streams receiving non‐point source pollution from agriculture may be able to support higher densities of Hydropsyche, which may further reduce the suitability of these habitats for B. appalachia. 7. This experimental study suggests that competition may complicate interpretation of biotic indices, as changes in benthic invertebrate community structure normally ascribed to pollution may arise from intra‐specific competition.     

Volatile pheromone signalling in Drosophila

Once captured by the antenna, the male‐specific pheromone 11‐cis vaccenyl acetate (cVA) binds to an extracellular binding protein called LUSH that undergoes a conformational shift upon cVA binding. The stable LUSH–cVA complex is the activating ligand for pheromone receptors present on the dendrites of the aT1 neurones, comprising the only class of neurones that detect volatile cVA pheromone. This mechanism can explain the single molecule sensitivity of pheromone detection. The receptor that recognizes activated LUSH consists of a complex of several proteins, including Or67d, a member of the tuning odourant receptor family, Orco, a co‐receptor ion channel, and SNMP, a CD36 homologue that may be an inhibitory subunit. In addition, genetic screens and reconstitution experiments reveal additional factors that are important for pheromone detection. Identification and functional dissection of these factors in Drosophila melanogaster Meigen should permit the identification of homologous factors in pathogenic insects and agricultural pests, which, in turn, may be viable candidates for novel classes of compounds to control populations of target insect species without impacting beneficial species.     

Flood effects on invertebrates, sediments and particulate organic matter in the hyporheic zone of a gravel-bed stream

1. We investigated the effects of a flood on the fauna and physical habitat of the hyporheic zone of the Kye Burn, a fourth order gravel‐bed stream in New Zealand. 2. Freeze core hyporheic samples (to 50 cm depth) and benthic samples (to 10 cm) were taken, along with measurements of vertical hydrological gradient, before, 2 days after and 1 month after the flood (estimated return period: 1.5 years, estimated Q_max = 10.4 m³ s^?1). 3. The composition of the hyporheos differed over the three sampling occasions with fewer taxa collected immediately postflood than preflood. The equitability of the community was higher on both postflood occasions, consistent with the reduced densities of two abundant taxa (Leptophlebiidae and Copepoda). 4. Total invertebrate abundance was lower on the postflood occasions than preflood in both benthic (0–10 cm) and hyporheic (10–50 cm) sediments. Several taxa, including asellotan isopods and amphipods, recovered within 1 month of the event. Hyporheic densities of larval Hydora and nematodes did not differ among the three sampling occasions, but the water mite Pseudotryssaturus was more abundant 1 month after the flood than preflood. There was no evidence of vertical movements (to 50 cm) by any taxa in response to the flood. 5. The proportion of fine sediments (<1 mm) in the subsurface sediments (10–50 cm) increased over the three sampling occasions and median particle size declined, but sediment porosity did not change. More particulate organic matter was found in the sediments after the flood. 6. Our study provides little evidence that the hyporheic zone (to 50 cm) acted as a significant refuge during the flood event, although movements to or recolonisation from sediments deeper than 50 cm could explain the recovery of many crustacean and mite taxa within 1 month.