Maternal Investment Influences Expression of Resource Polymorphism in Amphibians: Implications for the Evolution of Novel Resource-Use Phenotypes

Maternal effects—where an individual's phenotype is influenced by the phenotype or environment of its mother—are taxonomically and ecologically widespread. Yet, their role in the origin of novel, complex traits remains unclear. Here we investigate the role of maternal effects in influencing the induction of a novel resource-use phenotype. Spadefoot toad tadpoles, Spea multiplicata, often deviate from their normal development and produce a morphologically distinctive carnivore-morph phenotype, which specializes on anostracan fairy shrimp. We evaluated whether maternal investment influences expression of this novel phenotype. We found that larger females invested in larger eggs, which, in turn, produced larger tadpoles. Such larger tadpoles are better able to capture the shrimp that induce carnivores. By influencing the expression of novel resource-use phenotypes, maternal effects may play a largely underappreciated role in the origins of novelty

Consistent Paternity Skew through Ontogeny in Peron's Tree Frog (Litoria peronii)

BackgroundA large number of studies in postcopulatory sexual selection use paternity success as a proxy for fertilization success. However, selective mortality during embryonic development can lead to skews in paternity in situations of polyandry and sperm competition. Thus, when assessment of paternity fails to incorporate mortality skews during early ontogeny, this may interfere with correct interpretation of results and subsequent evolutionary inference. In a previous series of in vitro sperm competition experiments with amphibians (Litoria peronii), we showed skewed paternity patterns towards males more genetically similar to the female.Methodology/Principal FindingsHere we use in vitro fertilizations and sperm competition trials to test if this pattern of paternity of fully developed tadpoles reflects patterns of paternity at fertilization and if paternity skews changes during embryonic development. We show that there is no selective mortality through ontogeny and that patterns of paternity of hatched tadpoles reflects success of competing males in sperm competition at fertilization.Conclusions/SignificanceWhile this study shows that previous inferences of fertilization success from paternity data are valid for this species, rigorous testing of these assumptions is required to ensure that differential embryonic mortality does not confound estimations of true fertilization success.<br /

Age and size at maturity: sex, environmental variability and developmental thresholds

In most organisms, transitions between different life-history stages occur later and at smaller sizes as growth conditions deteriorate. Day and Rowe recently proposed that this pattern could be explained by the existence of developmental thresholds (minimum sizes or levels of condition below which transitions are unable to proceed). The developmental-threshold model predicts that the reaction norm of age and size at maturity will rotate in an anticlockwise manner from positive to a shallow negative slope if: (i) initial body size or condition is reduced; and/or (ii) some individuals encounter poor growth conditions at increasingly early developmental stages. We tested these predictions by rearing replicated populations of soil mites Sancassania berlesei (Michael) under different growth conditions. High-food environments produced a vertical relationship between age and size at maturity. The slope became increasingly shallow as food was reduced. By contrast, high food in the maternal environment reduced the slope of the reaction norm of age and size at maturity, whereas low food increased it. Overall, the reaction norm of age and size at maturity in S. berlesei was significantly nonlinear and differed for males and females. We describe how growth conditions, mother's environment and sex determine age and size at maturity in S. berlesei

Disentangling Ancient Interactions: A New Extinct Passerine Provides Insights on Character Displacement among Extinct and Extant Island Finches

11 páginas, 5 figuras, 1 tabla.[Background]Evolutionary studies of insular biotas are based mainly on extant taxa, although such biotas represent artificial subsets of original faunas because of human-caused extinctions of indigenous species augmented by introduced exotic taxa. This makes it difficult to obtain a full understanding of the history of ecological interactions between extant sympatric species. Morphological bill variation of Fringilla coelebs and F. teydea (common and blue chaffinches) has been previously studied in the North Atlantic Macaronesian archipelagos. Character displacement between both species has been argued to explain bill sizes in sympatry. However, this explanation is incomplete, as similar patterns of bill size have been recorded in F. coelebs populations from islands with and without F. teydea.[Methodology/Principal Findings]The discovery of a new extinct species in Tenerife (Canary Islands), here named Carduelis aurelioi n. sp. (slender-billed greenfinch), provides the opportunity to study ancient ecological interactions among Macaronesian finches. To help understand the evolutionary histories of forest granivores in space and time, we have performed a multidisciplinary study combining: (1) morphological analyses and radiocarbon dating (11,460±60 yr BP) of the new taxon and, (2) molecular divergence among the extant finch species and populations in order to infer colonization times (1.99 and 1.09 My for F. teydea and F. coelebs respectively).[Conclusion/Significance]C. aurelioi, F. coelebs and F. teydea co-habited in Tenerife for at least one million years. The unique anatomical trends of the new species, namely chaffinch-like beak and modified hind and forelimbs, reveal that there was a process of divergence of resource competition traits among the three sympatric finches. The results of our study, combined with the presence of more extinct greenfinches in other Macaronesian islands with significant variation in their beak sizes, suggests that the character displacement has influenced patterns of divergence in bill size and shape on other Macaronesian islands as well.Peer reviewe

Does the definition of a novel environment affect the ability to detect cryptic genetic variation?

AbstractAnthropogenic change exposes populations to environments that have been rare or entirely absent from their evolutionary past. Such novel environments are hypothesized to release cryptic genetic variation, a hidden store of variance that can fuel evolution. However, support for this hypothesis is mixed. One possible reason is a lack of clarity in what is meant by ‘novel environment’, an umbrella term encompassing conditions with potentially contrasting effects on the exposure or concealment of cryptic variation. Here, we use a meta‐analysis approach to investigate changes in the total genetic variance of multivariate traits in ancestral versus novel environments. To determine whether the definition of a novel environment could explain the mixed support for a release of cryptic genetic variation, we compared absolute novel environments, those not represented in a population's evolutionary past, to extreme novel environments, those involving frequency or magnitude changes to environments present in a population's ancestry. Despite sufficient statistical power, we detected no broad‐scale pattern of increased genetic variance in novel environments, and finding the type of novel environment did not explain any significant variation in effect sizes. When effect sizes were partitioned by experimental design, we found increased genetic variation in studies based on broad‐sense measures of variance, and decreased variation in narrow‐sense studies, in support of previous research. Therefore, the source of genetic variance, not the definition of a novel environment, was key to understanding environment‐dependant genetic variation, highlighting non‐additive genetic variance as an important component of cryptic genetic variation and avenue for future research.</jats:p

Unbiased Transcriptional Comparisons of Generalist and Specialist Herbivores Feeding on Progressively Defenseless Nicotiana attenuata Plants

Background Herbivore feeding elicits dramatic increases in defenses, most of which require jasmonate (JA) signaling, and against which specialist herbivores are thought to be better adapted than generalist herbivores. Unbiased transcriptional analyses of how neonate larvae cope with these induced plant defenses are lacking. Methodology/Principal Findings We created cDNA microarrays for Manduca sexta and Heliothis virescens separately, by spotting normalized midgut-specific cDNA libraries created from larvae that fed for 24 hours on MeJA-elicited wild-type (WT) Nicotiana attenuata plants. These microarrays were hybridized with labeled probes from neonates that fed for 24 hours on WT and isogenic plants progressively silenced in JA-mediated defenses (N: nicotine; N/PI: N and trypsin protease inhibitors; JA: all JA-mediated defenses). H. virescens neonates regulated 16 times more genes than did M. sexta neonates when they fed on plants silenced in JA-mediated defenses, and for both species, the greater the number of defenses silenced in the host plant (JA > N/PI > N), the greater were the number of transcripts regulated in the larvae. M. sexta larvae tended to down-regulate while H. virescens larvae up- and down-regulated transcripts from the same functional categories of genes. M. sexta larvae regulated transcripts in a diet-specific manner, while H. virescens larvae regulated a similar suite of transcripts across all diet types. Conclusions/Significance The observations are consistent with the expectation that specialists are better adapted than generalist herbivores to the defense responses elicited in their host plants by their feeding. While M. sexta larvae appear to be better adapted to N. attenuata's defenses, some of the elicited responses remain effective defenses against both herbivore species. The regulated genes provide novel insights into larval adaptations to N. attenuata's induced defenses, and represent potential targets for plant-mediated RNAi to falsify hypotheses about the process of adaptation

Is the Relationship between Body Size and Trophic Niche Position Time-Invariant in a Predatory Fish? First Stable Isotope Evidence

Characterizing relationships between individual body size and trophic niche position is essential for understanding how population and food-web dynamics are mediated by size-dependent trophic interactions. However, whether (and how) intraspecific size-trophic relationships (i.e., trophic ontogeny pattern at the population level) vary with time remains poorly understood. Using archival specimens of a freshwater predatory fish Gymnogobius isaza (Tanaka 1916) from Lake Biwa, Japan, we assembled a long-term (>40 years) time-series of the size-dependence of trophic niche position by examining nitrogen stable isotope ratios (δ15N) of the fish specimens. The size-dependence of trophic niche position was defined as the slope of the relationship between δ15N and log body size. Our analyses showed that the slope was significantly positive in about 60% of years and null in other years, changing through time. This is the first quantitative (i.e., stable isotope) evidence of long-term variability in the size-trophic relationship in a predatory fish. This finding had implications for the fish trophic dynamics, despite that about 60% of the yearly values were not statistically different from the long-term average. We proposed hypotheses for the underlying mechanism of the time-varying size-trophic relationship

Stress Resistance and Longevity Are Not Directly Linked to Levels of Enzymatic Antioxidants in the Ponerine Ant Harpegnathos saltator

BACKGROUND: The molecular mechanisms of variations in individual longevity are not well understood, even though longevity can be increased substantially by means of diverse experimental manipulations. One of the factors supposed to be involved in the increase of longevity is a higher stress resistance. To test this hypothesis in a natural system, eusocial insects such as bees or ants are ideally suited. In contrast to most other eusocial insects, ponerine ants show a peculiar life history that comprises the possibility to switch during adult life from a normal worker to a reproductive gamergate, therewith increasing their life expectancy significantly. RESULTS: We show that increased resistance against major stressors, such as reactive oxygen species and infection accompanies the switch from a life-history trait with normal lifespan to one with a longer life expectancy. A short period of social isolation was sufficient to enhance stress resistance of workers from the ponerine ant species Harpegnathos saltator significantly. All ant groups with increased stress resistances (reproducing gamergates and socially isolated workers) have lower catalase activities and glutathione levels than normal workers. Therewith, these ants resemble the characteristics of the youngest ants in the colony. CONCLUSIONS: Social insects with their specific life history including a switch from normal workers to reproducing gamergates during adult life are well suited for ageing research. The regulation of stress resistance in gamergates seemed to be modified compared to foraging workers in an economic way. Interestingly, a switch towards more stress resistant animals can also be induced by a brief period of social isolation, which may already be associated with a shift to a reproductive trajectory. In Harpegnathos saltator, stress resistances are differently and potentially more economically regulated in reproductive individuals, highlighting the significance of reproduction for an increase in longevity in social insects. As already shown for other organisms with a long lifespan, this trait is not directly coupled to higher levels of enzymatic and non-enzymatic antioxidants

The complete mitochondrial genome of the broad-winged damselfly <i>Mnais costalis</i> Selys (Odonata: Calopterygidae) obtained by next-generation sequencing

<p>We used next-generation sequencing to characterise the complete mitochondrial genome of the damselfly <i>Mnais costalis</i> (Odonata, Calopterygidae). Illumina paired end reads were mapped against COI and 16S sequences from <i>M. costalis</i> and then extended using an iterative <i>de novo</i> map procedure. The final assembly was a contiguous sequence of 15,487 bp, which contained all standard mitochondrial coding regions and the putative A+T rich region. The gene configuration of the <i>M. costalis</i> mitogenome is similar to that of other odonates, comprising 13 protein-coding genes, large and small rRNA genes, and 22 tRNA genes. We found three intergenic spacers that are also present in all available whole odonate mitogenomes. Base composition of the <i>M. costalis</i> mitogenome is 40% (A), 20% (C), 14% (G) and 26% (T), with a high A+T content (66%). The characterisation of the complete mitochondrial genome of <i>M. costalis</i> adds to the growing list of mitogenomes currently available for odonates, and will help to improve primer design for future population genetic studies. A phylogenetic analysis including the currently available mitochondrial genome sequences of odonates suggests that <i>Epiophlebia superstes</i> is more closely related to the Zygoptera than to the Anisoptera.</p

Quantifying multivariate genotype-by-environment interactions, evolutionary potential and its context-dependence in natural populations of the water flea,<i>Daphnia magna</i>

ABSTRACT Genotype-by-environment interactions (G x E) underpin the evolution of plastic responses in natural populations. Theory assumes that G x E interactions exist but empirical evidence from natural populations is equivocal and difficult to interpret because G x E interactions are normally univariate plastic responses to a single environmental gradient. We compared multivariate plastic responses of 43 Daphnia magna clones from the same population in a factorial experiment that crossed temperature and food environments. Multivariate plastic responses explained more than 30% of the total phenotypic variation in each environment. G x E interactions were detected in most environment combinations irrespective of the methodology used. However, the nature of G x E interactions was context-dependent and led to environment-specific differences in additive genetic variation (G-matrices). Clones that deviated from the population average plastic response were not the same in each environmental context and there was no difference in whether clones varied in the nature (phenotypic integration) or magnitude of their plastic response in different environments. Plastic responses to food were aligned with additive genetic variation ( g max) at both temperatures, whereas plastic responses to temperature were not aligned with additive genetic variation ( g max) in either food environment. These results suggest that fundamental differences may exist in the potential for our population to evolve novel responses to food versus temperature changes, and challenges past interpretations of thermal adaptation based on univariate studies