Avian predation on a parasitic fly of cervids during winter: can host‐related cues increase the predation risk?

The deer ked (Lipoptena cervi) is an ectoparasitic fly on cervids that has expanded its distribution rapidly in Northern Europe. However, the regulating biotic factors such as predation remain unknown. The host‐independent pupal stage of the fly lasts for several months. Blackish pupae are visible against snow, especially on the bedding sites of hosts, and are thus exposed to predators. To evaluate the role of predation on the invasion dynamics and evolution of L. cervi, we monitored pupal predation on artificial bedding sites in three geographical areas in Finland during winter. We explored: (1) possible predators; (2) magnitude of predation; and (3) whether predation risk is affected by host‐derived cues. We demonstrate that pupae are predated by a number of tit species. Any reddish brown snow discoloration on bedding sites, indicating heavy infestation of the host, serves as an exploitable cue for avian predators, thereby increasing the risk of pupal predation. The ability of tits to use this host‐derived cue seems to be dependent on the prevalence of L. cervi and the period of invasion history, which suggests that it may be a learned behavioural response. Predation by tits may potentially affect the L. cervi population dynamics locally. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 275–286.     

Genome size rather than content might affect call properties in toads of three ploidy levels (Anura: Bufonidae: Bufo viridis subgroup)

In vertebrates, genome size has been shown to correlate with nuclear and cell sizes, and influences phenotypic features, such as brain complexity. In three different anuran families, advertisement calls of polyploids exhibit longer notes and intervals than diploids, and difference in cellular dimensions have been hypothesized to cause these modifications. We investigated this phenomenon in green toads (Bufo viridis subgroup) of three ploidy levels, in a different call type (release calls) that may evolve independently from advertisement calls, examining 1205 calls, from ten species, subspecies, and hybrid forms. Significant differences between pulse rates of six diploid and four polyploid (3n, 4n) green toad forms across a range of temperatures from 7 to 27 °C were found. Laboratory data supported differences in pulse rates of triploids vs. tetraploids, but failed to reach significance when including field recordings. This study supports the idea that genome size, irrespective of call type, phylogenetic context, and geographical background, might affect call properties in anurans and suggests a common principle governing this relationship. The nuclear‐cell size ratio, affected by genome size, seems the most plausible explanation. However, we cannot rule out hypotheses under which call‐influencing genes from an unexamined diploid ancestral species might also affect call properties in the hybrid‐origin polyploids. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 584–590.     

Convergent evolutionary processes driven by foraging opportunity in two sympatric morph pairs of Arctic charr with contrasting post‐glacial origins

The expression of two or more discrete phenotypes amongst individuals within a species (morphs) provides multiple modes upon which selection can act semi‐independently, and thus may be an important stage in speciation. In the present study, we compared two sympatric morph systems aiming to address hypotheses related to their evolutionary origin. Arctic charr in sympatry in Loch Tay, Scotland, exhibit one of two discrete, alternative body size phenotypes at maturity (large or small body size). Arctic charr in Loch Awe segregate into two temporally segregated spawning groups (breeding in either spring or autumn). Mitochondrial DNA restriction fragment length polymorphism analysis showed that the morph pairs in both lakes comprise separate gene pools, although segregation of the Loch Awe morphs is more subtle than that of Loch Tay. We conclude that the Loch Awe morphs diverged in situ (within the lake), whereas Loch Tay morphs most likely arose through multiple invasions by different ancestral groups that segregated before post‐glacial invasion (i.e. in allopatry). Both morph pairs showed clear trophic segregation between planktonic and benthic resources (measured by stable isotope analysis) but this was significantly less distinct in Loch Tay than in Loch Awe. By contrast, both inter‐morph morphological and life‐history differences were more subtle in Loch Awe than in Loch Tay. The strong ecological but relatively weak morphological and life‐history divergence of the in situ derived morphs compared to morphs with allopatric origins indicates a strong link between early ecological and subsequent genetic divergence of sympatric origin emerging species pairs. The emergence of parallel specialisms despite distinct genetic origins of these morph pairs suggests that the effect of available foraging opportunities may be at least as important as genetic origin in structuring sympatric divergence in post‐glacial fishes with high levels of phenotypic plasticity. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

The influence of large wood on brown trout (Salmo trutta) behaviour and surface foraging

1. Changes in riparian vegetation owing to forest harvesting may affect the input of large wood, a major structural element, to streams. Studies of large wood impacts on stream fish have focused on population‐level responses, whereas little attention has been given to how wood affects fish behaviour. 2. In a laboratory stream experiment, we tested how two size classes of brown trout, Salmo trutta, (mean size of 85 and 125 mm), alone and together, responded to a gradient of large wood in terms of activity, foraging on terrestrial drift and interactions between conspecifics. 3. The results showed that the presence of large wood significantly reduced the overall activity of the fish, the number of agonistic interactions between individuals and the proportion of captured prey. However, activity decreased relatively more than the proportion of captured prey, resulting in a significant positive net effect of wood on the number of prey captures per time spent active (PTA). This indicates that trout living in habitats with high wood density may have a higher net energy gain than trout living in habitats with less wood. 4. There were no observable size‐class differences in the benefits of large wood or in the utilisation of surface‐drifting terrestrial prey. 5. These results suggest that the presence of large wood may be an important factor shaping stream communities and that a lack of structural complexity may decrease energy gain, increase agonistic interactions and, consequently, lower the production of brown trout.     

Fungi are involved in the effects of litter mixtures on consumption by shredders

1. Decomposition of litter mixtures in both terrestrial and aquatic ecosystems often shows non‐additive diversity effects on decomposition rate, generally interpreted in streams as a result of the feeding activity of macroinvertebrates. The extent to which fungal assemblages on mixed litter may influence consumption by macroinvertebrates remains unknown. 2. We assessed the effect of litter mixing on all possible three‐species combinations drawn from four tree species (Alnus glutinosa, Betula pendula, Juglans regia and Quercus robur) on both fungal assemblages and the rate of litter consumption by a common shredder, Gammarus fossarum. After a 9‐week inoculation in a stream, batches of leaf discs were taken from all leaf species within litter mixture combinations. Ergosterol, an indicator of fungal biomass, and the composition of fungal assemblages, assessed from the conidia released, were determined, and incubated litter offered to G. fossarum in a laboratory‐feeding experiment. 3. Mixing leaf litter species enhanced both the Simpson’s index of the fungal assemblage and the consumption of litter by G. fossarum, but had no clear effect on mycelial biomass. Specifically, consumption rates of J. regia were consistently higher for mixed‐species litter packs than for single‐species litter. In contrast, the consumption rates of B. pendula were not affected by litter mixing, because of the occurrence of both positive and negative litter‐mixing effects in different litter species combinations that counteracted each other. 4. In some litter combinations, the greater development of some fungal species (e.g. Clavariopsis aquatica) as shown by higher sporulation rates coincided with increased leaf consumption, which may have resulted from feeding preferences by G. fossarum for these fungi. 5. Where litter mixture effects on decomposition rate are mediated via shredder feeding, this could be due to indirect effects of the fungal assemblage.     

Spatial and Temporal Analysis of Contact Rates in Female White-Tailed Deer

Abstract: White-tailed deer (Odocoileus virginianus) are important game mammals and potential reservoirs of diseases of domestic livestock; thus, diseases of deer are of great concern to wildlife managers. Contact, either direct or indirect, is necessary for disease transmission, but we know little about the ecological contexts that promote intrasexual contact among deer. Using pair-wise direct contacts estimated from Global Positioning System collar locations and joint utilization distributions (JUDs), we assessed habitats in which contacts occur to test whether direct contact rates among female white-tailed deer in different social groups differs among land-cover types. We also tested whether contact rates differed among seasons, lunar phases, and times of day. We obtained locations from 27 female deer for periods of 0.5–17 months during 2002–2006. We designated any simultaneous pair of locations for 2 deer <25 m apart as a direct contact. For each season, we used compositional analysis to compare land-cover types where 2 deer had contact to available land-cover weighted by their JUD. We used mixed-model logistic regression to test for effects of season, lunar phase, and time of day on contact rates. Contact rates during the gestation season were greater than expected from random use in forest and grassland cover, whereas contact rates during the fawning period were greater in agricultural fields than in other land-cover types. Contact rates were greatest during the rut and lowest in summer. Diel patterns of contact rates varied with season, and contact rates were elevated during full moon compared to other lunar periods. Both spatial and temporal analyses suggest that contact between female deer in different social groups occurs mainly during feeding, which highlights the potential impact of food distribution and habitat on contact rates among deer. By using methods to associate contacts and land-cover, we have created beneficial tools for more elaborate and detailed studies of disease transmission. Our methods can offer information necessary to develop spatially realistic models of disease transmission in deer.     

Estimation of Occupied and Unoccupied Black-Tailed Prairie Dog Colony Acreage in Colorado

Abstract: Black-tailed prairie dogs (Cynomys ludovicianus) are a species of concern and accurate estimates of occupied area are required to assess their status. We conducted aerial line-intercept surveys to estimate colony areas in Colorado, USA, 2006–2007. Optimal allocation based on results from a previous (2002) survey was used to distribute flight time to sample 28 counties. Uncorrected estimates of active and inactive colony areas from the aerial surveys were 329,529 (SE=16,841) ha and 18,292 (SE=2,366) ha, respectively. We attempted to ground-truth a randomly selected sample of 186 colony intercepts but gained complete access to only 150. Ground-truthing demonstrated that aerial surveys estimated only 96% of the true lengths of colony intercepts but overestimated the proportion of active colonies. Corrected estimates of active and inactive colony areas are 319,165 (SE = 20,105) ha and 42,422 (SE = 11,485) ha, respectively. Because ground-truthing was not conducted in the original 2002 survey, uncorrected estimates from this survey are the appropriate metric to be used for comparison to the 2002 data. Our estimates demonstrated a 29% increase (SE = 6.3) in area occupied since surveys were conducted in 2002. These results are useful to state and federal agencies and other conservation partners in determining the condition of the species when conducting status reviews.     

Soft‐tissue imprints in fossil and Recent cephalopod septa and septum formation

Several soft‐tissue imprints and attachment sites have been discovered on the inside of the shell wall and on the apertural side of the septum of various fossil and Recent ectocochleate cephalopods. In addition to the scars of the cephalic retractors, steinkerns of the body chambers of bactritoids and some ammonoids from the Moroccan and the German Emsian (Early Devonian) display various kinds of striations; some of these striations are restricted to the mural part of the septum, some start at the suture and terminate at the anterior limit of the annular elevation. Several of these features were also discovered in specimens of Mesozoic and Recent nautilids. These structures are here interpreted as imprints of muscle fibre bundles of the posterior and especially the septal mantle, blood vessels as well as the septal furrow. Most of these structures were not found in ammonoids younger than Middle Devonian. We suggest that newly formed, not yet mineralized (or only slightly), septa were more tightly stayed between the more numerous lobes and saddles in more strongly folded septa of more derived ammonoids and that the higher tension in these septa did not permit soft‐parts to leave imprints on the organic preseptum. It is conceivable that this permitted more derived ammonoids to replace the chamber liquid faster by gas and consequently, new chambers could be used earlier than in other ectocochleate cephalopods, perhaps this process began even prior to mineralization. This would have allowed faster growth rates in derived ammonoids.