Hyperpigmentation of Chinchilla Stria Vascularis Following Acoustic Trauma

This report describes morphological alterations of the chinchilla stria vascularis seen 30 days after exposure to impulse noise. The observed changes included a dramatic increase in strial melanin content which occurred in 7 of 36 animals exposed to electronically synthesized impulses presented in various temporal patterns at either 135 or 150 dB peak SPL. In these animals, densely pigmented areas of stria 1.5 to 3 mm in length were found in the basal cochlear turn. Light and electron microscopic study revealed that these areas contained large numbers of melanin granules situated primarily in pale-staining cells of the middle layer of the stria. Unlike the pigment granules present in normal chinchilla stria, the melanosomes found in the noise-exposed material clearly showed ultrastructural features characteristic of eumelanin. Melanin granules were also observed in marginal and basal cells of the noise-exposed stria. In some cases, pigment granules which had apparently been expelled from the marginal cells were present in the endolymphatic space beneath Reissner's membrane and on the strial surface. These findings support the view that the melanin-bearing cells of the inner ear are capable of markedly increased activity in response to stressful conditions.     

Positive indirect effect of aquatic insects on terrestrial prey is not offset by increased predator density

1. Changes in one prey species' density can indirectly affect the abundance of another prey species if a shared predator eats both species. Sometimes, indirect effects occur when prey straddle habitats, including when riparian predator populations grow in response to emergent aquatic insects and increase predation on terrestrial prey. However, predators may largely switch to aquatic insects or become satiated, reducing predation on terrestrial prey. 2. To determine the net indirect effect of aquatic insects on terrestrial arthropods via generalist spider predators, a field experiment was conducted mimicking midge influx and a wolf spider numerical response inside enclosures near an Icelandic lake. Lab mesocosms were also used to assess per capita rates of spider predation u nder differing levels of midge abundance. 3. Midges always decreased sentinel prey predation, but this effect increased with predator density. When midges were absent, predation increased 30% at a high spider density, but predation was equal between spider treatments when midges were present. In situ arthropods showed no effect of midge or spider treatments, although non‐significant abundance patterns were observed congruent with sentinel prey results. 4. In lab mesocosms, prey survivorship increased ≥50% where midges were present and rapidly saturated; the addition of 5, 20, 50, and 100 midges equivalently reduced spider predation, supporting predator distraction rather than satiation as the root cause. 5. The present results demonstrate a strong positive indirect effect of midges and broadly support the concept that predator responses to alternative prey are a major influence on the magnitude and direction of predator‐mediated indirect effects.     

Terrestrial deposition of aquatic insects increases plant quality for insect herbivores and herbivore density

1. Mobile organisms such as emergent aquatic insects can subsidise land with aquatic nutrients, creating a link between terrestrial and aquatic ecosystems. 2. Deposition of aquatic insects on land produces bottom‐up effects in arthropod detritivore communities and may also affect plants and plant–herbivore interactions. 3. To investigate the effects of insect deposition on plant–herbivore interactions, we conducted a field experiment and surveys of tealeaf willow (Salicaceae; Salix phylicifolia Coste) and July highflyer caterpillars (Geometridae; Hydriomena furcata Thunberg) at lakes in Northeast Iceland with either high‐ or low‐midge density and deposition to land. 4. It was found that willow at high‐midge lakes had 8–11% higher nitrogen content compared with willow at low‐midge lakes. In addition, natural caterpillar density was 4–6 times higher and caterpillars were 72% heavier at high‐midge lakes than low‐midge lakes. 5. A fully reciprocal caterpillar transplant experiment among willow at high‐ and low‐midge lakes was performed to separate the influence of habitat and midge effects on caterpillar performance. 6. After transplant, pupae of July Highflyer caterpillars were on average 11% heavier at high‐midge sites compared with low‐midge sites. However, this difference was not statistically significant. 7. The present findings indicate that cross‐ecosystem subsidies in the form of aquatic insects can increase plant foliar quality and the abundance of insect herbivores in recipient ecosystems.     

Biocontrol potential varies with changes in biofuel–crop plant communities and landscape perenniality

We examined the potential local‐ and landscape‐level impacts of different biofuel production systems on biocontrol, an important service provided by arthropod natural enemies. Specifically, we sampled natural enemies with sweep nets and measured predation of sentinel pest eggs in stands of corn, switchgrass and mixed prairie in Michigan and Wisconsin (total n=40 for natural enemy sampling, n=60 for egg predation), relating them to crop type, forb cover and diversity, and the composition and heterogeneity of the surrounding landscape. Grasslands with intermediate levels of forb cover and flower diversity supported two‐orders of magnitude more natural enemy biomass, fourfold more natural enemy families, and threefold greater rates of egg predation than corn. Data suggest this was in part due to a general increase in biomass, richness and predation in perennial grasslands compared with corn, combined with a positive effect of intermediate levels of forb cover and flower diversity. Specifically, natural enemy biomass and family richness showed hump‐shaped relationships to forb cover that peaked in sites with 5–25% forbs, while egg predation increased with floral diversity. At the landscape scale, both natural‐enemy biomass and egg predation increased with the area of forest in the landscape, and egg predation almost doubled as the area of herbaceous, perennial habitats within 1.5 km of study sites increased. Our results suggest that floristically diverse, perennial grasslands support diverse and abundant predator communities that contribute to natural pest suppression. In addition, large‐scale production of biofuel crops could positively or negatively affect biocontrol services in agricultural landscapes through associated changes in the area of perennial habitats. Biofuel landscapes that incorporate perennial grasslands could support a variety of beneficial organisms and ecosystem services in addition to producing biomass.     

Stable isotopes reveal different patterns of inter‐crop dispersal in two ladybeetle species

1. Dispersal plays a key role in structuring the local population densities of many insect species, yet the movement patterns across the landscape of most species are poorly understood. By measuring the stable isotope of carbon (δ¹³C) from multiple tissues, a novel approach applied to field‐collected insects, we were able to infer differences in movement patterns of two species of mobile generalist insect predators. 2. Coccinella septempunctata L (7‐spot ladybeetle) and Harmonia axyridis Pallas (multicoloured Asian ladybeetle) were collected in agricultural habitats in 2003 and 2004, and were assayed for δ¹³C in the elytra (slow turnover) and fat/reproductive tissues (fast turnover). δ¹³C values were used to infer diet use of C3 versus C4 crops. 3. Coccinella septempunctata was relatively more faithful to a particular habitat and tended to stay in alfalfa and soybean (C3‐based photosynthetic crops) over long periods during the summer. This contrasts with H. axyridis which showed isotopic evidence consistent with frequent late‐season movement between C3 and C4 crops such as corn in the landscape. 4. These differing patterns suggest that in the late summer season H. axyridis individuals traverse the environment more extensively and utilise broadly dispersed aphid resources, whereas C. septempunctata adults are more specialised on alfalfa and soybean crops.     

Phylogeography of Parnassius apollo: hints on taxonomy and conservation of a vulnerable glacial butterfly invader

Parnassius apollo (Linnaeus, 1758) is probably the most renowned Eurasian montane butterfly. Its specialized ecology makes it very sensitive to habitat and climate changes, so that it is now experiencing range contraction and local extinction across most of its range. We sequenced 869 bp of the mitochondrial DNA (mtDNA) cytochrome oxidase I gene in 78 P. apollo populations (201 individuals) in order to: (1) assess the phylogeographic pattern of the species; (2) shed light on the historical biogeographic processes that shaped the distribution of the species; and (3) identify geographic population units of special value for the conservation of the species' genetic diversity. Our analyses revealed a very strong phylogeographic structure in P. apollo, which displays a number of distinctive mtDNA lineages populating geographically distinct areas. Overall sequence divergence is relatively shallow, and is consistent with a recent (late Pleistocene) colonization of most of the range. We propose that P. apollo is best viewed as an atypical glacial invader in southern and western Europe, the isolated, montane populations of which, threatened by climate warming, retain a large fraction of the species evolutionary heritage. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 169–183.