Quickie well done: no evidence of physiological costs in the development race of Lucilia sericata necrophagous larvae

The present study focuses on trade-offs between the development rates and their life-history traits of feeding larvae. Indeed, quick growth is considered to be vital for necrophagous insects such as larvae because they are part of a rapidly changing ecosystem and at the mercy of many predators. However, excessively quick growth can have a negative effect on other life-history traits (e.g. survivorship and body size). The blowfly Lucilia sericata (Diptera: Calliphoridae) is used in the present study because this species is frequently found on carcasses in Central Europe and is a well-known experimental model in insect physiology and ecology. Individuals are reared from first instars to adults at two different constant temperatures (i.e. 15 and 28 °C) and under three different conditions: 100 Lucilia sericata (i.e. small monospecific condition), 250 L. sericata (i.e. large monospecific) or 125 L. sericata + 125 Calliphora vicina (i.e. heterospecific). The development time, pupal and larval survival rate and pupal size are determined individually under each condition. Regarding size and development time, substantial variation is observed between the different growth conditions and within a larval group under the same conditions. However, no trade-offs between development rate and size or survival are detected. These results demonstrate that, under the range of developmental conditions tested in the present study, the quick development of L. sericata larvae does not affect their size or mortality. This developmental plasticity may explain the evolutionary success of this species, which is present in several ecosystems worldwide and dominates the fresh-carrion ecosystem.     

Asymmetric competition between larvae of the blowflies Calliphora vicina and Lucilia sericata in carrion

1. The relative abundance of the blowflies Calliphora vicina (R.-D.) and Lucilia sericata (Meigen) in carrion was considered in relation to inter- and intraspecific larval competition and the distribution of adults between habitat types. 2. In mixed and pure laboratory cultures of L. sericata and C. vicina the mortality of both species increased and adult size declined as the initial larval number was increased. However, for L. sericata at initial numbers greater than ten larvae/g of liver, the effects of competition on adult size and mortality were greater in the mixed cultures than in the pure cultures. In contrast, for C. vicina at numbers greater than ten larvae/g of liver, the effects of competition on adult size and mortality were greater in the pure cultures than in the mixed cultures. 3. The laboratory data suggest therefore that for L. sericata the effects of interspecific competition with C. vicina on size and mortality were greater than the effects of intraspecific competition in a pure culture at the same initial number. Notably, however, the intensity of interspecific competition was not sufficiently asymmetric to allow C. vicina to exclude L. sericata even at the highest numbers examined. 4. In the field, higher numbers of adult L. sericata emerged from the carcasses of laboratory mice placed in open pasture than in woodland or hedgerow sites. In contrast, higher numbers of C. vicina emerged from carcasses placed in woodland and hedgerow sites. 5. Trapping showed that in the field adult L. sericata were relatively more abundant in open pasture than in woodland and hedgerow sites, while C. vicina were more abundant in woodland and hedgerow sites than in open pasture. 6. It is concluded that the low numbers of L. sericata that emerge from carrion relative to the numbers of C. vicina may, in part, be the result of asymmetric interspecific competition, but that the uneven distribution of adults of the two species among habitat types also plays a major role in shaping the blowfly community in carrion.     

Can Ingestion of Lead Shot and Poisons Change Population Trends of Three European Birds: Grey Partridge,Common Buzzard,and Red Kite?

Little is known about the magnitude of the effects of lead shot ingestion alone or combined with poisons (e.g., in bait or seeds/granules containing pesticides) on population size, growth, and extinction of non-waterbird avian species that ingest these substances. We used population models to create example scenarios demonstrating how changes in these parameters might affect three susceptible species: grey partridge (Perdix perdix), common buzzard (Buteo buteo), and red kite (Milvus milvus). We added or subtracted estimates of mortality due to lead shot ingestion (4–16% of mortality, depending on species) and poisons (4–46% of mortality) reported in the UK or France to observed mortality of studied populations after models were calibrated to observed population trends. Observed trends were decreasing for partridge (in continental Europe), stable for buzzard (in Germany), and increasing for red kite (in Wales). Although lead shot ingestion and poison at modeled levels did not change the trend direction for the three species, they reduced population size and slowed population growth. Lead shot ingestion at modeled rates reduced population size of partridges by 10%, and when combined with bait and pesticide poisons, by 18%. For buzzards, decrease in mean population size by lead shot and poisons combined was much smaller (≤ 1%). The red kite population has been recovering; however, modeled lead shot ingestion reduced its annual growth rate from 6.5% to 4%, slowing recovery. If mortality from poisoned baits could be removed, the kite population could potentially increase at a rapid annual rate of 12%. The effects are somewhat higher if ingestion of these substances additionally causes sublethal reproductive impairment. These results have uncertainty but suggest that declining or recovering populations are most sensitive to lead shot or poison ingestion, and removal of poisoned baits can have a positive impact on recovering raptor populations that frequently feed on carrion.     

Biogeographical patterns of variation in Western European populations of the great green bush-cricket (Tettigonia viridissima; Orthoptera Tettigoniidae)

The great green bush-cricket, Tettigonia viridissima, is at the northern limits of its geographic distribution in the UK and has suffered a significant reduction in population abundance and range over the last 50 years, now being largely confined to the southern UK. This study uses five characters to investigate differences between UK and mainland Western European populations, questioning the possibility that UK populations might represent a distinct species or sub-species and thus deserve special conservation status. Males of T. viridissima from UK, France and Spain were compared using morphometry, flight, male calling song and analysis of mitochondrial DNA sequences. Results suggest morphological differences between UK population samples and continental Europe with the UK samples showing shorter wing length relative to body length than populations in continental Europe. Morphological differences between French and Spanish populations followed a size cline related to latitude with more southerly populations showing larger features. Analysis of male flight distances and calling song showed significant differences with increased flight distance and minimum stridulation following a southerly latitude which correlates with wing length results. No differences consistent with geographical distributions were found in mitochondrial DNA COI sequence alignments. Morphological differences could be due to developmental differences linked to differing temperature clines or a non-adaptive difference caused by the colonisation history of the species. The consequences of morphometric variation on flight function and stridulation in bush-crickets are discussed.     

The postglacial history of Scots pine (Pinus sylvestris L.) in western Europe: evidence from mitochondrial DNA variation

The geographical structure of mitochondrial (mt)DNA variants (mitotypes) was investigated in 38 western European populations of Scots pine Pinus sylvestris using restriction fragment length polymorphism (RFLP) analysis of total DNA and a homologous cox1 probe. Three major mitotypes (designated a, b and d ) were detected. Within Spain all three major mitotypes were found, gene diversity was high, H_T = 0.586, and this diversity was distributed predominantly among rather than within populations (F_ST(M) = 0.813 for the seven Spanish populations). Mitotype d was present only in the most southerly population from the Sierra Nevada . Elsewhere in Europe, populations showed little or no mtDNA diversity within regions, but there were marked differences between regions. Italian populations were fixed for mitotype b ; populations from northern France, Germany, Poland, Russia and southern Sweden were fixed for mitotype a ; while populations in northern Fennoscandia were fixed for mitotype b . The isolated Scottish populations were predominantly of mitotype a , but mitotype b was present in three of the 20 populations scored. In Scotland, UK gene diversity (H_T = 0.120) and genetic differentiation among populations (F_ST(M) = 0.37) was much lower than in Spain. When interpreted in the light of complementary data from pollen analysis and nuclear genetic markers, the results suggest that present-day populations of P. sylvestris in western Europe have been derived from at least three different sources after glaciation.     

Possible effects of ingested lead gunshot on populations of ducks wintering in the UK

Although the use of lead ammunition for shooting wildfowl and/or over listed wetlands in the UK has been banned, c. 70% of ducks shot in England (the only UK country with compliance monitoring) are still shot with lead and the proportion of ducks found dead with signs of lead poisoning from ingested gunshot has not declined significantly since the ban. However, there is little quantitative evidence of the impacts of additional mortality from lead poisoning on duck populations. For the eight duck species that winter in freshwater habitats in the UK, we found that inter‐specific variation in mean population growth rate during the period 1990/1991 to 2013/2014 was significantly negatively correlated with two independent measures of the prevalence of ingested lead gunshot in the UK and Europe. This relationship was found for a wide range of different periods over which population growth was estimated, and also for annual growth rates in the period 1966/1967 to 2013/2014, derived from smoothed population trajectories. These findings support the hypothesis that ingested lead gunshot might affect population trend. An alternative hypothesis, that migratory short‐stopping driven by climate change affected trends in numbers of ducks wintering in the UK, was not supported by simple or partial correlation results. The possible impact of ingested lead gunshot on the Common Pochard Aythya ferina, a species listed as globally threatened, is of special concern.     

Oviposition preferences and antennal size in carrion flies

Carrion-feeding flies use odours emanating from the decomposing corpse as cues for oviposition and are described as generalists because the larvae feed on the corpses of diverse species. Whereas several features of the corpse may influence the oviposition choices of these flies, it is not known whether there is a preference for a particular species of corpse. We provided carrion flies with ovipositional (and feeding) choices in a field experiment, in which various odour sources were presented simultaneously. We found novel evidence of broadly consistent choices of carrion by flies from four families. Traps baited with decaying fish flesh captured the greatest number of individuals, whereas traps baited with decaying pig liver typically attracted the least. We also asked whether individuals captured in the various baits vary in antennal size, perhaps reflecting different capacities for odour detection. There was a trend for individuals of Lucilia sericata Meigen (Diptera: Calliphoridae) and the platystomatid collected from the traps baited with pig liver to have significantly larger antennae, whereas individuals of Muscina stabulans (Fallen) (Diptera: Muscidae) captured in traps baited with marine fish flesh had relatively longer antennae for their body size. Our data reveal a more nuanced pattern of oviposition behaviour in these generalist carrion flies, which may reflect differences in their preference of carrion with different nutrients, and in their capacity to detect particular odours.     

Effets d'un régulateur de croissance d'insectes,le fénoxycarbe,sur la diapause du psylle du poirier Cacopsylla pyri

The nature of the responses of the sheep blowfly Lucilia sericata Meigen (Diptera: Calliphoridae) to carrion odours and carbon dioxide were examined in a windtunnel in the laboratory and the attractiveness of carrion-bait was examined in the field. In the wind tunnel, gravid 9-day-old females increased both the number and duration of their flights, in response to carrion odours. In addition, linear velocity was reduced and the sinuosity of flight increased in the presence of these odours. With 3-day-old females, the response to carrrion odour depended on previous exposure to proteinaceous material. Protein deprived females showed kinetic responses to carrionodour which were similar to those of gravid females. No such changes were observed in protein-fed females. No responses to CO₂ were observed. In the field, the importance of olfactory cues in bait location was demonstrated by the absence of L. sericata from sticky targets lacking an odour bait. Increased bait concentration did not affect the age, sex ratio or ratio of L. sericata to other Lucilia spp. caught, but did increase the numbers caught. Analysis of the reproductive status of females caught, indicated that a greater number of gravid females were caught than expected, while a lower number of females in the final stages of vitellogenesis were caught than expected. The results show that the responses of L. sericata to odours are complex, and are dependent on both exogenous and endogenous stimuli, the latter including the stage of ovarian development.     

Bimodal cue complex signifies suitable oviposition sites to gravid females of the common green bottle fly

Gravid females of the common green bottle fly, Lucilia sericata Meigen (Diptera: Calliphoridae), readily locate recently deceased vertebrates as oviposition sites, particularly when these animals have been injured. We investigated semiochemical and visual cues that mediate attraction of gravid females to fresh rat carrion. Female flies were more strongly attracted to incised rat carrion than to intact carrion. They were also attracted to Porapak Q headspace volatile (HSV) extract of incised rat carrion. Analyzing aliquots of Porapak Q HSV extract by gas chromatographic‐electroantennographic detection revealed nine components [phenol, para‐ and/or meta‐cresol (could not be separated), guaiacol, dimethyl trisulfide (DMTS), phenylacetaldehyde, (E)‐2‐octenal, nonanal, and tetramethyl pyrazine] that consistently elicited responses from blow fly antennae. In laboratory experiments, a synthetic blend of these nine components was as attractive to gravid females as Porapak Q HSV extract, but blend attractiveness was due entirely to DMTS. In both laboratory and field experiments, increasing doses of DMTS attracted increasingly more flies. Coupled with DMTS, carrion‐type color cues (dark red, black) were more effective than bright color cues (white, yellow) in attracting flies. In field experiments, dark traps baited with DMTS captured a total of 214 calliphorid flies (200 L. sericata, 10 Lucilia illustris Meigen, three Calliphora vicina Robineau‐Desvoidy, one Calliphora vomitoria L.), all of which were gravid females. These results support the conclusion that DMTS and dark color represent a bimodal cue complex that signifies suitable oviposition sites to gravid calliphorid females, particularly L. sericata.     

Population suppression for control of the blowfly Lucilia sericata and sheep blowfly strike

Abstract.

• 1 The control of ovine myiasis by suppression of populations of the blowfly Lucifia sericata was investigated experimentally on three farms in the south-west of England in 1992 and 1993.
• 2 In blind trials, sheep on one farm (control) were given two doses of placebo, on a second two doses of the larvicide cyromazine (Vetrazin®, CibaGeigy), and on a third cyromazine and a subsequent dose of placebo.
• 3 The first treatment was given shortly before the predicted spring emergence of L.sericata and the second shortly before the predicted emergence of the second generation. Previous simulation analysis had identified strategic early-season treatment as the optimum for blowfly population suppression.
• 4 On both treatment farms significantly smaller L.sericata populations were recorded throughout 1992 and the incidence of strike was significantly lower than on the control farm. The results show that appropriate early-season timing of sheep treatment can suppress populations of L.sericata and could be used by farmers to reduce the incidence of blowfly strike.
• 5 The results suggest, however, that the effectiveness of population suppression and strike incidence may have been influenced by immigration into the control areas and by adverse weather, the latter changing the susceptibility of sheep to strike and resulting in rising strike incidence even when L.sericata population densities were low. In practice, therefore, blowfly population suppression should be employed as a component of an integrated strike management programme.

     

HYBRID ZONE DYNAMICS ARE INFLUENCED BY GENOTYPE-SPECIFIC VARIATION IN LIFE-HISTORY TRAITS: EXPERIMENTAL EVIDENCE FROM HYBRIDIZING GAMBUSIA SPECIES

Results from two experiments are presented that contrast differences in life-history traits and population dynamics between two species of live bearing fishes (Gambusia affinis and G. holbrooki) that hybridize across portions of the southeastern United States. Progeny from parental holbrooki and holbrooki-affinis F₁ crosses exhibited larger lengths at birth, at 15 days, and matured earlier, and at larger size than did progeny from parental affinis and affinis-holbrooki F₁ crosses. Comparisons of experimental populations of affinis, holbrooki, and mixed (affinis + holbrooki) species composition followed over two years revealed that affinis populations consistently exhibited smaller population size, lower carrying capacity, lower recruitment, and larger over-winter mortality than did holbrooki or mixed populations. Evidence for density-dependent reductions in fecundity and concomitant increases in juvenile mortality rates were observed in all populations, but were most pronounced for affinis populations. Genotype-specific differences in life-history traits appear to confer differential advantage to offspring of parental holbrooki origin and F, progeny of holbrooki maternal parentage given the resource availability and the age structure and densities experienced during these experiments. Results have direct implications regarding the rate and direction of evolution within hybrid zones formed by these two species.     

Frequency and intensity of drought stress alters the population size and dynamics of Elatobium abietinum on Sitka spruce

The green spruce aphid, Elatobium abietinum, is the most important defoliating pest of Sitka spruce, Picea sitchensis, in the UK. Populations are expected to increase in response to predicted climate change, therefore placing Sitka spruce under increased risk of widespread and severe defoliation. The effect of spring–summer drought stress on E. abietinum population dynamics and development over multiple years was assessed in a field experiment under five different drought treatments with differing intensities and frequencies. The impact on host tolerance, in terms of needle retention, was also investigated. No differences in the length of time taken to reach peak population size were observed. Despite this, E. abietinum populations were found to respond positively to low amplitude intermittent stress, with high densities maintained for longer after the peak. Spring peak densities of aphids did not differ among drought levels, although an autumn peak was observed consistently over 2 years on trees subjected to continuous severe drought. This suggested advancement in the onset of Sitka spruce dormancy. Aphid infestation significantly increased percentage needle loss under all drought treatments, although no differences were observed between drought levels. An interaction between aphid presence and drought treatment was, however, observed during a second year of drought where no aphids were present. The study herein presented has contributed to the understanding of E. abietinum population responses under a changing climate. The implications for damage to host Sitka spruce are of relevance to forest management strategies, as an increase in drought events are predicted in the UK.     

Influence of seasonal time constraints on growth and development of common frog tadpoles: a photoperiod experiment

Organisms living in seasonal environments are often limited by the time available to complete their development. Especially individuals in northern populations may face severe time constraints in their need of completing development before the end of the growth season. Larval amphibians have been widely used in studies of phenotypic plasticity. However, their responses to changes in photoperiod, the main seasonal cue in many organisms, are unknown. In a laboratory experiment, we studied whether common frog (Rana temporaria) tadpoles originating from two populations (separated latitudinally by 1600 km) adjust their growth and development according to the progress of the season by using photoperiodic cues, and whether these responses are temperature dependent. We hypothesised that if frogs use photoperiod as a cue, they should increase growth and development rates as a response to photoperiodic treatments mimicking progressing season. Although our predictions were not verified in either of the populations, photoperiod manipulations had effects on larval life history in both populations. When exposed to progressing season treatments and high temperature, tadpoles from the southern population ceased feeding, which led to delayed metamorphosis and increased mortality. In the northern population, age at metamorphosis was unaffected by the photoperiod treatments, but growth rate until metamorphosis and metamorphic size were slightly larger in the treatments with shorter (increasing or decreasing) day length. Irrespective of photoperiod treatments, growth and development rates, size at metamorphosis and food consumption were higher in the northern as compared to the southern population. These results indicate that in contrast to several insect species, the critical life history decisions in amphibian larvae may not be strongly influenced by photoperiodic cues, but different populations seem to differ in this respect. However, the strong temperature×photoperiod interactions in several traits in the southern population suggest that the role of photoperiodic cues may be affected by other environmental factors, although the ecological significance of these differences remains unclear.     

Large-scale geographic patterns of genetic variation in Melica nutans, a widespread Eurasian woodland grass

 The geographic distribution of allozyme variation within the Eurasian boreo-nemoreal woodland grass Melica nutans L. has been investigated together with a minor subset of other Melica species. Twenty alleles were found at nine polymorphic loci in M. nutans. Allelic richness was highest in areas central in the species' European distribution, i.e. in southern Fennoscandia. High population densities, reducing the effects of genetic drift, as well as accumulation of variation through long-distance gene-flow from different marginal populations, is proposed to explain high allelic richness in this area. Several alleles showed geographic patterns in distribution and frequency variation. However, these patterns were not congruent, e.g. some alleles appear to have migrated to northern Europe from the south-west whereas others may have spread from the east. Genetic distances between geographic regions, each consisting of 2–6 populations, were generally low between all Fennoscandian, Russian and Siberian regions, but much higher between western and continental European regions. On the population level, cluster analysis grouped populations from Siberia, Russia, coastal and lowland areas in Fennoscandia and British Cumbria into one subcluster whereas other subclusters contained mainly south-west European populations or populations from almost throughout the distribution range. A scenario with several independent glacial refugia in central Europe, south-western Siberia and possibly western Norway, and subsequent colonisation of Fennoscandia mainly from the east, but with some long-distance gene-flow from central Europe, is proposed. Received April 3, 2002; accepted September 17, 2002 Published online: December 11, 2002     

DENSITY-DEPENDENT EVOLUTION OF LIFE-HISTORY TRAITS IN DROSOPHILA MELANOGASTER

Populations of Drosophila melanogaster were maintained for 36 generations in r- and K-selected environments in order to test the life-history predictions of theories on density-dependent selection. In the r-selection environment, populations were reduced to low densities by density-independent adult mortality, whereas populations in the K-selection environment were maintained at their carrying capacity. Some of the experimental results support the predictions or r- and K-selection theory; relative to the r-selected populations, the K-selected populations evolved an increased larval-to-adult viability, larger body size, and longer development time at high larval densities. Mueller and Ayala (1981) found that K-selected populations also have a higher rate of population growth at high densities. Other predictions of the thoery are contradicted by the lack of differences between the r and K populations in adult longevity and fecundity and a slower rate of development for r-selected individuals at low densities. The differences between selected populations in larval survivorship, larval-to-adult development time, and adult body size are strongly dependent on larval density, and there is a significant interaction between populations and larval density for each trait. This manifests an inadequacy of the theory on r- and K-selection, which does not take into account such interactions between genotypes and environments. We describe mechanisms that may explain the evolution of preadult life-history traits in our experiment and discuss the need for changes in theories of density-dependent selection.     

Population genetic structure of the endangered crayfish Austropotamobius pallipes in France based on microsatellite variation: biogeographical inferences and conservation implications

1. One important goal in conservation biology is to characterise evolutionary lineages within endangered species before management decisions are taken. Here, we assess population differentiation in the freshwater crayfish Austropotamobius pallipes, an endangered species endemic to western Europe and provide valuable information for the conservation of French populations. 2. Analysis of five microsatellite loci in 44 populations revealed very different within population levels of genetic diversity (0.000 < H₀ < 0.564). Two groups, corresponding to northern and southern French populations, showed a high degree of genetic differentiation in both allele frequencies and allele sizes. Comparison of these results with previous studies of A. pallipes strongly suggests that the divergence between northern and southern populations could have occurred during the last glaciation period of the Pleistocene from one Atlantic and one Mediterranean refuge. 3. Evidence for genetic admixture between these two lineages was revealed by correspondence analyses in southern populations, probably as the result of artificial translocations. 4. French populations appeared significantly differentiated among the different river drainages and were highly structured within rivers. The impact of population size, population bottlenecks and founder events on the population genetic differentiation are discussed. 5. Based on these results, we propose the designation of two evolutionarily significant units for A. pallipes in France. Our data also support the maintenance of separate demographic management strategies for crayfish inhabiting different river systems. However, genetic analyses will have to be combined with demographic and ecological data for sustainable conservation programmes.     

An analysis of population genetic differentiation and genotype–phenotype association across the hybrid zone of carrion and hooded crows using microsatellites and MC1R

The all black carrion crow ( Corvus corone corone ) and the grey and black hooded crow ( Corvus   corone cornix ) meet in a narrow hybrid zone across Europe. To evaluate the degree of genetic differentiation over the hybrid zone, we genotyped crows from the centre and edges of the zone, and from allopatric populations in northern (Scotland–Denmark–Sweden) and southern Europe (western–central northern Italy), at 18 microsatellites and at a plumage candidate gene, the MC1R gene. Allopatric and edge populations were significantly differentiated on microsatellites, and populations were isolated by distance over the hybrid zone in Italy. Single-locus analyses showed that one locus, CmeH9, differentiated populations on different sides of the zone at the same time as showing only weak separation of populations on the same side of the zone. Within the hybrid zone there was no differentiation of phenotypes at CmeH9 or at the set of microsatellites, no excess of heterozygotes among hybrids and low levels of linkage disequilibrium between markers. We did not detect any association between phenotypes and nucleotide variation at MC1R , and the two most common haplotypes occurred in very similar frequencies in carrion and hooded crows. That we found a similar degree of genetic differentiation between allopatric and edge populations irrespectively of their location in relation to the hybrid zone, no differentiation between phenotypes within the hybrid zone, and neither heterozygote excess nor consistent linkage disequilibrium in the hybrid zone, is striking considering that carrion and hooded crows are phenotypically distinct and sometimes recognised as separate species.     

Ecological predictors of reduced avian reproductive investment in the southern hemisphere

Despite intensive research, the factors driving spatial patterns in life‐history traits remain poorly understood. One of the most frequently documented, and paradoxically, least understood patterns, is the latitudinal gradient of increasing avian clutch size at higher latitudes. These gradients are less marked in the southern hemisphere, thus clutch sizes tend to be smaller at southern latitudes than at equivalent northern ones. We exploited a natural experiment provided by the introduction of European passerines to New Zealand (NZ) to test three widely proposed ecological drivers of this pattern, i.e. the nest predation, Ashmole’s seasonality, and the breeding density hypotheses. We focus on the blackbird Turdus merula and the song thrush T. philomelos as founder effects do not have a major influence on the reproductive traits of their introduced populations. Both species laid smaller clutches in NZ than in Europe. These reductions had stabilised within one hundred years and were not associated with a compensatory increase in investment in individual offspring by laying larger eggs. In contrast to the nest predation hypothesis, daily nest predation rates were lower in NZ than in Europe. Smaller southern hemisphere clutches were associated with higher conspecific population densities and a relaxation of seasonal clutch size trends. These findings thus provide some support for both Ashmole’s seasonality and the breeding density hypotheses. Analyses across 11 European passerines introduced to NZ suggest, however, that neither of these hypotheses provide general explanations of smaller clutches in the southern hemisphere. We suggest that reduced seasonality and lower nest predation promote increased breeding densities and adult survival in the southern hemisphere. The later may drive smaller southern clutch sizes by generating spatial variation in the outcome of the trade‐off between reproductive investment and longevity.     

Neglected native or undesirable alien? Resolution of a conservation dilemma concerning the pool frog Rana lessonae

Introduced species often pose serious threats to biodiversity, but occasionally confusion arises as to whether a species really is introduced or is in fact an overlooked native. A recent UK conservation dilemma has centred on the status of the pool frog Rana lessonae. This species has been the subject of documented introductions from central and southern Europe since the early 1800s, the accepted position being that all UK R. lessonae populations are descended from these introductions. However, a closer examination of early UK literature sources, and recent discoveries of isolated, native R. lessonae populations in Sweden and Norway, led some herpetologists to question whether the species was in fact present as a native at some locations prior to the introductions. Research was initiated along four major lines of enquiry: genetic, bioacoustic, archaeozoological and archival. A high degree of convergence among the genetic and bioacoustic investigations demonstrated that the potentially native UK pool frogs were closely related to Scandinavian frogs, thus ruling out introductions from further south as a potential origin. Subfossil evidence of pool frogs was found from ca. 1000 years before present, demonstrating that the species occurred in the UK prior to known introductions. Archival sources produced no historical support for introductions from northern Europe. The postglacial history inferred for these northern populations is consistent with the known climatic and geographical conditions. Taken together, the evidence for the native status of the pool frog is compelling, and furthermore the UK population appears to be part of a distinct northern clade.     

The effects of population density and lake characteristics on growth and size structure of brook trout Salvelinus fontinalis (Mitchill, 1815) in boreal forest lakes in Canada

This paper examines the effect of lake characteristics on population density and how this variation affects growth, mortality and population size structure of brook trout, Salvelinus fontinalis. The study was conducted on 17 recreationally fished, reproductively isolated boreal forest lakes in Newfoundland, Canada from 1993 to 2000. A standardized sampling program, the Fyke Littoral Index Netting program (FLIN) was used to collected data that describes brook trout population parameters and life history attributes. Regression analyses showed significant relationships between fish density and biomass and characteristics of the lakes. Variation in fish density and biomass was explained by lake surface area and littoral habitat area. Significant relationships were found when growth, mortality and size structure were regressed against density. The proportional stock distribution and theoretical maximum size of brook trout were negatively related to density, and natural mortality was positively related to density. The largest maximum length and highest proportional stock densities occurred at brook trout densities of less than 30 fish/ha. In general, the higher the proportion of littoral habitat area the higher the densities of brook trout, which correspondingly had important effects on growth, natural mortality and size structure of the brook trout populations. This information is critical to the development of management strategies aimed at altering size distribution to produce specific fisheries management outcomes.