The effects of acid episodes on Lepomis sunfish recruitment and growth in two ponds in Massachusetts, U.S.A.

1. The effects of transient acidity on the recruitment of Lepomis sunfish were examined in two ponds in Plymouth County, Massachusetts with on-site monitoring systems. One pond had low buffering capacity and was sensitive to acidification and acid spikes, the other had better buffering with no acid spikes. Pond pH was continuously monitored over 3 years.
2. Young-of-the-year (YOY) sunfish were collected and through otolith analysis aged in days since larval metamorphosis. Day-classes were constructed from these age data. The YOY swim-up day-class distribution was more irregular with pronounced gaps in Maquan Pond than in the better-buffered Furnace Pond.
3. The poorly buffered pond, Maquan, experienced irregular acid spikes, defined as a sudden lowering of pond pH from about 6.6 to below 5.3 for an hour or more. These spikes were associated with rainfall ( P < 0.005). Acid spikes were not found at Furnace Pond.
4. The occurrence of acid spikes and diminished day-classes from expected swim-up values were significantly associated, based on pooled data from 3 years at Maquan Pond.
5. Transient acid spikes at Maquan Pond appear to harm Lepomis YOY at the vulnerable stage of metamorphosis, when their gills become fully functional and exposed to the environment.
6. Growth rates of Lepomis YOY were also studied. Length–age and weight–length growth relationships were examined for differences in instantaneous growth coefficients between years and between ponds. Length–age instantaneous growth coefficients ranged from 0.0114 to 0.0176 over five pond-years. The slowest growth rates were in a warm, dry spawning season with the earliest average metamorphosis date.     

Response of littoral invertebrates to reduction of fish density: simultaneous experiments in ponds with different fish assemblages

1. We experimentally reduced densities of predatory fish in replicated 2 m² areas of the littoral zone in two ponds to test whether density and biomass of invertebrates would respond to release from fish predation. The ponds are of similar size and in close proximity, but support different fish assemblages: bluegills ( Lepomis macrochirus Rafinesque) and largemouth bass ( Micropterus salmoides (Lacepede)) in one pond, and bluespotted sunfish ( Enneacanthus gloriosus (Holbrook)) and chain pickerel ( Esox niger Lesueur) in the other. Fish densities were reduced to less than 15% of ambient levels in both experiments.
2. In the bluegill–bass pond, density and biomass of most invertebrate taxa and size classes were unaffected by the fish manipulation. Total invertebrate densities did not differ significantly between fish treatments, but total invertebrate biomass was significantly greater where fish density was reduced, averaging 30% higher over the course of the study. Likewise, manipulation of fish in the bluespotted sunfish–pickerel pond had few significant effects on individual taxa and size classes. There were no significant effects on total invertebrate abundance in the bluespotted sunfish–pickerel pond.
3. Our results provide direct experimental evidence consistent with the collective evidence from previous work, suggesting that the impact of fish predation on density and biomass of invertebrate prey in littoral habitats is variable, but generally weak. Invertebrates that coexist successfully with fish in littoral systems probably are adept at taking advantage of refugia offered by the structurally complex physical environment.     

Induced carbon reallocation and compensatory growth as root herbivore tolerance mechanisms

Upon attack by leaf herbivores, many plants reallocate photoassimilates below ground. However, little is known about how plants respond when the roots themselves come under attack. We investigated induced resource allocation in maize plants that are infested by the larvae Western corn rootworm Diabrotica virgifera virgifera. Using radioactive ¹¹CO₂, we demonstrate that root‐attacked maize plants allocate more new ¹¹C carbon from source leaves to stems, but not to roots. Reduced meristematic activity and reduced invertase activity in attacked maize root systems are identified as possible drivers of this shoot reallocation response. The increased allocation of photoassimilates to stems is shown to be associated with a marked thickening of these tissues and increased growth of stem‐borne crown roots. A strong quantitative correlation between stem thickness and root regrowth across different watering levels suggests that retaining photoassimilates in the shoots may help root‐attacked plants to compensate for the loss of belowground tissues. Taken together, our results indicate that induced tolerance may be an important strategy of plants to withstand belowground attack. Furthermore, root herbivore‐induced carbon reallocation needs to be taken into account when studying plant‐mediated interactions between herbivores.     

Isolation and characterization of EST‐derived microsatellite loci from the fungal wheat pathogen Phaeosphaeria nodorum

Eleven polymorphic microsatellite loci and one minisatellite locus originating from expressed sequence tag (EST) libraries of Phaeosphaeria (syn. Stagonospora) nodorum were isolated and characterized. The satellite markers were used to genotype isolates from field populations collected in China, North America and South Africa. The number of alleles per locus ranged from two to 15. Genotype diversity ranged from 87.5 to 95.3 and gene diversity from 0.1 to 0.8. The variable levels of polymorphism within and among populations of P. nodorum renders these 12 satellite loci ideal markers for population genetic analysis of P. nodorum.     

Climate change and faunal dynamics in the uttermost part of the earth

To use the ‘lessons of the Pleistocene’ to forecast the biotic effects of climate change, we must parse the effects of history and ecology in the Quaternary record. The preponderance of Northern Hemisphere studies of biotic responses to climate change provides a limited set of players and environmental circumstances with which to decouple these drivers. In this issue Lessa et al. (2010) examine population structure in 14 species of mice distributed across Patagonia and Tierra del Fuego in southern South America. In the Southern Cone, glacial ice was alpine, not polar; major habitats were (and are) oriented N–S, not E–W; and habitable land area actually increased, not decreased, at the height of the last glacial maximum (LGM). Despite these differences, there is evidence for poleward demographic expansion in 10 of the 14 species, and phylogeographic breaks in these are likewise stepped by latitude (and presumably history) rather than by biome. Nevertheless, high latitude endemism and the antiquity of these lineages point to an extended presence in the region that very likely predates the Pleistocene.     

A primitive anomodont therapsid from the base of the Beaufort Group (Upper Permian) of South Africa

Patranomodon nyaphulii , known from a nearly complete skull, lower jaw and partial postcranial skeleton, is morphologically the most primitive anomodont therapsid yet discovered. It is from the Eodicynodon Assemblage Zone, the lowest biozone of the Beaufort Group of South Africa, which has a primitive therapsid fauna comparable with that of the Russian Zone I. Patranaomodon is primitive with respect to other anomodonts in having short palatal exposure of the premaxilla, an unreduced tabular, a slit-like interpterygoidal vacuity, a screw-shaped jaw articulation (which precludes fore-aft sliding of the lower jaw), and only three sacral vertebrae. The poorly-known Galechirus and Galepus from the younger Cistecephalus Assemblage Zone appear to be at a comparably primitive evolutionary grade, and the three genera are tentatively united in the family Galechiridae. The taxon Dromasauria is shown to be paraphyletic and therefore should be discarded.     

Brown trout and food web interactions in a Minnesota stream

1. We examined indirect, community‐level interactions in a stream that contained non‐native brown trout (Salmo trutta Linnaeus), native brook trout (Salvelinus fontinalis Mitchill) and native slimy sculpin (Cottus cognatus Richardson). Our objectives were to examine benthic invertebrate composition and prey selection of fishes (measured by total invertebrate dry mass, dry mass of individual invertebrate taxa and relative proportion of invertebrate taxa in the benthos and diet) among treatments (no fish, juvenile brook trout alone, juvenile brown trout alone, sculpin with brook trout and sculpin with brown trout). 2. We assigned treatments to 1 m² enclosures/exclosures placed in riffles in Valley Creek, Minnesota, and conducted six experimental trials. We used three designs of fish densities (addition of trout to a constant number of sculpin with unequal numbers of trout and sculpin; addition of trout to a constant number of sculpin with equal numbers of trout and sculpin; and replacement of half the sculpin with an equal number of trout) to investigate the relative strength of interspecific versus intraspecific interactions. 3. Presence of fish (all three species, alone or in combined‐species treatments) was not associated with changes in total dry mass of benthic invertebrates or shifts in relative abundance of benthic invertebrate taxa, regardless of fish density design. 4. Brook trout and sculpin diets did not change when each species was alone compared with treatments of both species together. Likewise, we did not find evidence for shifts in brown trout or sculpin diets when each species was alone or together. 5. We suggest that native brook trout and non‐native brown trout fill similar niches in Valley Creek. We did not find evidence that either species had an effect on stream communities, potentially due to high invertebrate productivity in Valley Creek.     

A molecular-clock date for the origin of the animal phyla

Although the reliability of the molecular clock for determining divergence times that are not visible in the fossil record has been questioned, the amino-acid sequence differences in the α and β haemoglobins of a variety of living vertebrates do not support this view. While the molecular clock is clearly probabilistic rather than metronomic, it can be shown that the α and β haemoglobins have been evolving at a statistically equal rate since they first appeared some 450–500 million years ago. If this rate has always been constant for all globins, then the percentage sequence differences between several invertebrate and some vertebrate globins can be used to indicate that the initial radiation of the animal phyla occurred at least 900–1000 million years ago. ?Molecular evolution, Metazoa, haemoglobin.