Adaptive phenotypic plasticity and genetics of larval life histories in two Rana temporaria populations

Phenotypic plasticity provides means for adapting to environmental unpredictability. In terms of accelerated development in the face of pond-drying risk, phenotypic plasticity has been demonstrated in many amphibian species, but two issues of evolutionary interest remain unexplored. First, the heritable basis of plastic responses is poorly established. Second, it is not known whether interpopulational differences in capacity to respond to pond-drying risk exist, although such differences, when matched with differences in desiccation risk would provide strong evidence for local adaptation. We investigated sources of within- and among-population variation in plastic responses to simulated pond-drying risk (three desiccation treatments) in two Rana temporaria populations originating from contrasting environments: (1) high desiccation risk with weak seasonal time constraint (southern population); and (2) low desiccation risk with severe seasonal time constraint (northern population). The larvae originating from the environment with high desiccation risk responded adaptively to the fast decreasing water treatment by accelerating their development and metamorphosing earlier, but this was not the case in the larvae originating from the environment with low desiccation risk. In both populations, metamorphic size was smaller in the high-desiccation-risk treatment, but the effect was larger in the southern population. Significant additive genetic variation in development rate was found in the northern and was nearly significant in the southern population, but there was no evidence for genetic variation in plasticity for development rates in either of the populations. No genetic variation for plasticity was found either in size at metamorphosis or growth rate. All metamorphic traits were heritable, and additive genetic variances were generally somewhat higher in the southern population, although significantly so in only one trait. Dominance variances were also significant in three of four traits, but the populations did not differ. Maternal effects in metamorphic traits were generally weak in both populations. Within-environment phenotypic correlations between larval period and metamorphic size were positive and genetic correlations negative in both populations. These results suggest that adaptive phenotypic plasticity is not a species-specific fixed trait, but evolution of interpopulational differences in plastic responses are possible, although heritability of plasticity appears to be low. The lack of adaptive response to desiccation risk in northern larvae is consistent with the interpretation that selection imposed by shorter growing season has favored rapid development in north (approximately 8% faster development in north as compared to south) or a minimum metamorphic size at the expense of phenotypic plasticity.     

Reversibility of predator‐induced plasticity and its effect at a life‐history switch point

In natural systems, organisms are frequently exposed to spatial and temporal variation in predation risk. Prey organisms are known to develop a wide array of plastic defences to avoid being eaten. If inducible plastic defences are costly, prey living under fluctuating predation risk should be strongly selected to develop reversible plastic traits and adjust their defences to the current predation risk. Here, we studied the induction and reversibility of antipredator defences in common frog Rana temporaria tadpoles when confronted with a temporal switch in predation risk by dragonfly larvae. We examined the behaviour and morphology of tadpoles in experimental treatments where predators were added or withdrawn at mid larval development, and compared these to treatments with constant absence or presence of predators. As previous studies have overlooked the effects that developing reversible anti‐predator responses could have later in life (e.g. at life history switch points), we also estimated the impact that changes in antipredator responses had on the timing of and size at metamorphosis. In the presence of predators, tadpoles reduced their activity and developed wider bodies, and shorter and wider tails. When predators were removed tadpoles switched their behaviour within one hour to match that found in the constant environments. The morphology matched that in the constant environments in one week after treatment reversal. All these responses were highly symmetrical. Short time lags and symmetrical responses for the induction/reversal of defences suggest that a strategy with fast switches between phenotypes could be favoured in order to maximise growth opportunities even at the potential cost of phenotypic mismatches. We found no costs of developing reversible responses to predators in terms of life‐history traits, but a general cost of the induction of the defences for all the individuals experiencing predation risk during some part of the larval development (delayed metamorphosis). More studies examining the reversibility of plastic defences, including other type of costs (e.g. physiological), are needed to better understand the adaptive value of these flexible strategies.     

Genetic Polymorphism and Evolution in Parthenogenetic Animals. II. Diploid and Polyploid SOLENOBIA TRIQUETRELLA (Lepidoptera: Psychidae)

Genic polymorphism at sixteen enzyme loci of four different chromosomal races of Solenobia triquetrella (bisexual, two diploid parthenogenetic races and tetraploid parthenogenetic) has been studied by starch gel electrophoresis. Isolated small diploid bisexual populations have rather uniform allele frequencies at all loci which we have studied. Diploid and tetraploid parthenogenetic individuals of this species are in general as heterozygous as bisexual ones. All parthenogenetic local populations are different from each other in the Alps. These parthenogenetic genotypes cannot be derived from a common ancestor through single mutations but rather bear evidence for a polyphyletic origin of parthenogenesis in Solenobia triquetrella. In the marginal distribution areas of the species in northern Europe single genotypes are spread over far larger areas than in the mountain regions of central Europe. This may be due to the old origin of parthenogenesis and polyploidy in northern Europe. No new parthenogenetic and polyploid strains have lately arisen in the regions outside of the Alps.     

Female and male contribution to egg size in salmonids

Egg size contributes to other life history traits of an individual. It is traditionally considered as a maternally determined characteristic to which the male does not have any direct contribution. However, a recent finding in insects suggests that males can affect egg size also directly. In fish, the male effect could take place only during egg swelling, as the final egg size is reached after that. We studied egg size in four freshwater salmonid species (the land-locked Atlantic salmon, the brown trout, the Arctic charr and the lake trout) right after fertilisation (initial egg size) and after the swelling phase (final egg size). The results showed that the final egg size is affected not only by the initial egg size but also by both the female and the male through the process of egg swelling. This study suggests that paternal contribution may form a previously largely ignored source of variation in early life history traits in salmonid fish.     

Cytoskeletal structure of myoblasts with the mitochondrial DNA 3243A-->G mutation and of osteosarcoma cells with respiratory chain deficiency

The cytoskeleton, mainly composed of actin filaments, microtubules, and intermediate filaments, is involved in cell proliferation, the maintenance of cell shape, and the formation of cellular junctions. The organization of the intermediate filaments is regulated by phosphorylation and dephosphorylation. We examined cell population growth, apoptotic cell death, and the morphology of cytoskeletal components in myoblast cultures derived from patients with the 3243A-->G mutation in mitochondrial DNA (mtDNA) and from control subjects by means of assays detecting cellular nucleic acids, histone-associated DNA fragments and by immunolabeling of cytoskeletal components. Population growth was slower in the 3243A-->G myoblast cultures, with no difference in the amount of apoptotic cell death. The organization of vimentin filaments in myoblasts with 3243A-->G was disturbed by randomization of filament direction and length, whereas no disturbances were observed in the other cytoskeletal proteins. Vimentin filaments formed large bundles surrounding the nucleus in mtDNA-less (rho(0)) osteosarcoma cells and in osteosarcoma cells after incubation with sodium azide and nocodazole. We conclude that defects in oxidative phosphorylation lead to selective disruption of the vimentin network, which may have a role in the pathophysiology of mitochondrial diseases.     

Quantitative genetics of larval life-history traits in Rana temporaria in different environmental conditions

The degree to which genetic variation in a given trait varies among different populations of the same species and across different environments has seldom been quantified in wild vertebrate species. We investigated the expression of genetic variability and maternal effects in three larval life-history traits of the amphibian Rana temporaria. In a factorial laboratory experiment, five widely separated populations (max. 1600 km) were subjected to two different environmental treatments. Animal model analyses revealed that all traits were heritable (h(2) approximately 0.20) in all populations and under most treatment combinations. Although the cross-food treatment genetic correlations were close to unity, heritabilities under a restricted food regime tended to be lower than those under an ad libitum food regime. Likewise, maternal effects (m(2) approximately 0.05) were detected in most traits, and they tended to be most pronounced under restricted food conditions. We detected several cross-temperature genetic and maternal effects correlations that were lower than unity, suggesting that genotype-environment interactions and maternal effect-environment interactions are a significant source of phenotypic variation. The results reinforce the perspective that although the expression of genetic and maternal effects may be relatively homogeneous across different populations of the same species, local variation in environmental conditions can lead to significant variation in phenotypic expression of quantitative traits through genotype-environment and maternal effect-environment interactions.     

Elucidating the role of conserved glutamates in H+-pyrophosphatase of Rhodospirillum rubrum

H(+)-pyrophosphatase (H(+)-PPase) catalyzes pyrophosphate-driven proton transport against the electrochemical potential gradient in various biological membranes. All 50 of the known H(+)-PPase amino acid sequences contain four invariant glutamate residues. In this study, we use site-directed mutagenesis in conjunction with functional studies to determine the roles of the glutamate residues Glu(197), Glu(202), Glu(550), and Glu(649) in the H(+)-PPase of Rhodospirillum rubrum (R-PPase). All residues were replaced with Asp and Ala. The resulting eight variant R-PPases were expressed in Escherichia coli and isolated as inner membrane vesicles. All substitutions, except E202A, generated enzymes capable of PP(i) hydrolysis and PP(i)-energized proton translocation, indicating that the negative charge of Glu(202) is essential for R-PPase function. The hydrolytic activities of all other PPase variants were impaired at low Mg(2+) concentrations but were only slightly affected at high Mg(2+) concentrations, signifying that catalysis proceeds through a three-metal pathway in contrast to wild-type R-PPase, which employs both two- and three-metal pathways. Substitution of Glu(197), Glu(202), and Glu(649) resulted in decreased binding affinity for the substrate analogues aminomethylenediphosphonate and methylenediphosphonate, indicating that these residues are involved in substrate binding as ligands for bridging metal ions. Following the substitutions of Glu(550) and Glu(649), R-PPase was more susceptible to inactivation by the sulfhydryl reagent mersalyl, highlighting a role of these residues in maintaining enzyme tertiary structure. None of the substitutions affected the coupling of PP(i) hydrolysis to proton transport.     

Behavioural variation in Eurasian perch populations with respect to relative catchability

Animal personalities, i.e. consistent individual differences in behaviour, are currently of high interest among behavioural and evolutionary biologists. The topic has received increasing attention also in fisheries science because selective harvesting of certain behavioural types might impose fishing-induced selection on personality. Here, we ice-fished wild Eurasian perch (Perca fluviatilis) from three native populations and investigated whether differences in relative catchability would explain behavioural differences observed in experimental conditions. We inferred relative catchability differences indirectly by fishing each location first with generally inefficient artificial bait and then by more efficient natural bait. The captured, individually tagged fish were tested in groups for their exploration tendency, activity and boldness under authentic predation risk in semi-natural stream channels. Fish that were easily captured first with artificial bait expressed fast exploration and acute activity, whereas the fish captured with natural bait showed less active and explorative behaviour. Differences in relative catchability did not explain variation in boldness or body size. In conclusion, we found that (1) Eurasian perch differing in relative catchability differ in certain behavioural traits, (2) fast explorers are more common among fish that get easily caught compared to fish that are more difficult to catch, (3) relative catchability explains more behavioural variation in a novel environment than in a familiar one and (4) selectivity of recreational angling on fish behaviour may depend on applied angling method and the effort spent on each location.     

Restoring volume,diversity and continuity of deadwood in boreal forests

Restoration of boreal forests by emulating natural disturbances is used to bring back typical components of natural forests that are reduced by silvicultural management. The volume, diversity and continuity of deadwood are the most important factors determining the diversity of deadwood-dependent species. In a large-scale experiment consisting of 43 experimental stands and 15 controls we assessed how alternative restoration methods enhancing deadwood availability (felling and felling + burning with two levels of felling: 20 and 40 % of initial volume of living trees, and a storm treatment) would affect short- and long-term deadwood volume and diversity using 7-year deadwood measurements and simulation modelling. In short-term, restoration by felling + burning increased both the volume and diversity of deadwood, whereas felling only increased merely the volume of deadwood. The simulations of tree growth, mortality and wood decomposition indicated that in comparison to controls, felled and storm-treated stands have greater deadwood volumes up to 40 years and felled + burned stands more than 60 years after restoration. Our results suggest that felling with 20 % of initial tree volume does not harm the future deadwood continuity, whereas intensive burning may imperil the deadwood continuity in a stand level. In conclusion, restoration clearly speeds up the development of the deadwood volumes needed to host large portions of biodiversity, and burning is the most effective restoration method in short- and long term. In practice, several restoration methods could be used concurrently in the landscape to obtain the best results.