Variation In Life-history Traits Research Articles

Microbiome composition is shaped by geography and population structure in the parasitic wasp Asobara japonica, but not in the presence of the endosymbiont Wolbachia.

The microbial community composition is crucial for diverse life-history traits in many organisms. However, we still lack a sufficient understanding of how the host microbiome is acquired and maintained, a pressing issue in times of global environmental change. Here we investigated to what extent host genotype, environmental conditions, and the endosymbiont Wolbachia influence the bacterial communities in the parasitic wasp Asobara japonica. We sampled multiple wasp populations across 10 locations in their natural distribution range in Japan and sequenced the host genome (whole genome sequencing) and microbiome (16S rRNA gene). We compared the host population structure and bacterial community composition of wasps that reproduce sexually and are uninfected with Wolbachia with wasps that reproduce asexually and carry Wolbachia. The bacterial communities in asexual wasps were highly similar due to a strong effect of Wolbachia rather than host genomic structure. In contrast, in sexual wasps, bacterial communities appear primarily shaped by a combination of population structure and environmental conditions. Our research highlights that multiple factors shape the bacterial communities of an organism and that the presence of a single endosymbiont can strongly alter their compositions. This information is crucial to understanding how organisms and their associated microbiome will react in the face of environmental change.

Predator- and killed prey-induced fears bear significant cost to an invasive spider mite: Implications in pest management.

The success of biological control using predators is normally assumed to be achieved through direct predation. Yet it is largely unknown how the predator- and killed prey-induced stress to prey may contribute to biological control effectiveness. Here, we investigate variations in life-history traits and offspring fitness of the spider mite Tetranychus ludeni in response to cues from the predatory mite Phytoseiulus persimilis and killed T. ludeni, providing knowledge for evaluation of the nonconsumptive contribution to the biological control of T. ludeni and for future development of novel spider mite control measures using these cues. Cues from predators and killed prey shortened longevity by 23-25% and oviposition period by 35-40%, and reduced fecundity by 31-37% in T. ludeni females. These cues significantly reduced the intrinsic rate of increase (rm ) and net population growth rate (R0 ), and extended time to double the population size (Dt ). Predator cues significantly delayed lifetime production of daughters. Mothers exposed to predator cues laid significantly smaller eggs and their offspring developed significantly more slowly but these eggs had significantly higher hatch rate. Predator- and killed prey-induced fears significantly lower the fitness of T. ludeni, suggesting that these nonconsumptive effects can contribute to the effectiveness of biological control to a great extent. Our study provides critical information for evaluation of biological control effectiveness using predators and paves the way for identification of chemical odors from the predator and killed prey, and development of new materials and methods for the control of spider mite pests. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Phenotypic variation in Xenopus laevis tadpoles from contrasting climatic regimes is the result of adaptation and plasticity.

Phenotypic variations between populations often correlate with climatic variables. Determining the presence of phenotypic plasticity and local adaptation of a species to different environments over a large spatial scale can provide insight on the persistence of a species across its range. Amphibians, and in particular their larvae, are good models for studies of phenotypic variation as they are especially sensitive to their immediate environment. Few studies have attempted to determine the mechanisms that drive phenotypic variation between populations of a single amphibian species over a large spatial scale especially across contrasting climatic regimes. The African clawed frog, Xenopus laevis, occurs in two regions with contrasting rainfall regimes in southern Africa. We hypothesised that the phenotypic variation of life-history traits of X. laevis tadpoles emerges from a combination of plastic and genetic responses. We predictedthat plasticity wouldallow the development of tadpoles from both regions in each environment. We also predicted thatlocal adaptation of larval traits would drive the differentiation of reaction norms between populations and lower survival in tadpoles reared away from their home environment. We measured growth, time to metamorphosis, and survival in a reciprocal transplant experiment using outdoor mesocosms. Supporting our prediction, we found that the measured variation of all traits was explained by both adaptation and plasticity. However, the reaction norms differed between populations suggesting adaptive and asymmetric plasticity. All tadpoles experienced lower survival when translocated, but only translocated tadpoles from the winter rainfall region matched survival of local tadpoles. This has implications for the dynamics of translocated X. laevis into novel environments, especially from the winter rainfall region. Our discovery of their asymmetric capacity to overcome novel environmental conditions by phenotypic plasticity alone provides insight into their invasion success.

Patterns of biogeographic and regional life-history trait variation in four large-bodied tropical wrasses

Ectotherms display substantial demographic variation across latitudinal gradients of temperature. Higher temperatures are often associated with smaller size, rapid initial growth rates, and early maturation, generally described as the Temperature-Size Rule (TSR). The longevity of most ectotherms also declines at warmer, lower latitudes. However, these patterns may be modified by increases in food resources that can flow on to continuous growth and large adult size. The present study estimates age-based demographic parameters of large-bodied tropical wrasses (Hemigymnus melapterus, H. fasciatus, Cheilinus fasciatus, and Oxycheilinus digramma) collected from Philippine fish markets (9–11°N) and sampled from Palm (18.53–18.70°S) and Whitsunday (20.05–20.21°S) reefs on the Great Barrier Reef, Australia (GBR). Differences in longevity, initial growth rates, and the age at sexual maturation at a biogeographic scale, between the Philippines and GBR, conformed to predictions of the TSR. However, Philippine specimens exhibited greater relative body condition and sustained periods of growth beyond sexual maturity resulting in larger adult size than GBR samples. Size-structure data from Philippine marine reserves and fished sites indicated that these differences were not confounded by fishery-dependent sampling. Moreover, latitudinal length–weight relationships could not be explained by lower densities of the focal wrasses in the Philippines or by relative gonad size. Less pronounced patterns of demographic variation that differed across species were evident at a regional scale, among Palm and Whitsunday reefs. Patterns of demographic variation between the Philippines and GBR strongly suggest that differences in food resource levels will be important in explaining the observed geographic variation.

Life-history trait variation in native versus invasive asexual New Zealand mud snails.

Potamopyrgus antipodarum is a New Zealand freshwater snail that is invasive worldwide. While native P. antipodarum populations are characterized by frequent coexistence between obligately sexual and obligately asexual individuals, only the asexual snails are known to invade other ecosystems. Despitelow genetic diversity and the absence of sex, invasive asexual P. antipodarum are highly successful. Here, we quantified variation in three key life-history traits across invasive P. antipodarum lineages and compared this variation to already documented variation in these same traits in asexual native lineages to provide a deeper understanding of why some lineages become invasive. In particular, we evaluated if invasive lineages of P. antipodarum could be successful because they represent life-history variation from native ancestors that could facilitate invasion. We found that invasive snails displayed a non-representative sample of native diversity, with invasive snails growing more slowly and maturing more rapidly than their native counterparts. These results are consistent with expectations of a scenario where invasive lineages represent a subset of native variation that is beneficial in the setting of invasion. Together, these results help illuminate the mechanisms driving the worldwide expansion of invasive populations of these snails.

Can the Life History Trait Divergence of Two Extremes of a Cold-Water Genus Distribution Offer Evidence for Their Vulnerability to Sea Warming?

Cold- and deep-water species such as Molva species show low resilience to anthropogenic pressures, and they become particularly vulnerable at the warm edges of their distribution. In this study, the poorly documented Mediterranean ling (Molva macrophthalma) population from the northwestern Mediterranean Sea was analysed. This area is considered a cul-de-sac in a sea-warming hotspot, where M. macrophthalma shows a low population health status and is experiencing a climate-related reduction in abundance. Several life-history traits (length at maturity, reproductive cycle, fecundity style, oocyte recruitment pattern, and breeding strategy) are here described for the first time to evaluate the reproductive performance (oocyte diameter and production) in relation to the fish condition status (the HSI and relative condition index). Additionally, the results are compared with those of a population of a similar species, the blue ling (Molva dypterygia), inhabiting the cool edge of its distribution, hypothesised to have a higher condition status. Our results indicate that M. macrophthalma is a capital breeder with restricted secondary growth recruitment and group-synchronous oocyte development. In relative terms, the stressed southern M. macrophthalma exhibited a worse condition, a lower investment in reproduction, a smaller size at maturity, larger but fewer primary growth oocytes, and a smaller size-standardized production of secondary growth oocytes than the northern M. dypterygia. Significant differences in the secondary growth oocyte recruitment were also found. These findings reinforce the environment’s role in shaping the reproductive potential and condition status. Altogether, this study suggests high sensitivity to anthropogenic pressures for both species, and, especially for Mediterranean ling, it shows the importance of introducing monitoring and conservation measures to ensure the sustainability of its populations.

Geographic variation in reproductive investment of seven populations of male Brown frog (Rana kukunoris), endemic to the eastern Tibetan Plateau

Abstract Life-history theory suggests that male anurans living in harsh and unpredictable environmental conditions (e.g., low temperature and/or high seasonality) should decrease reproductive investment because of short periods of activity and poor productivity. Although geographic variations in female life-history traits have been investigated intensively across a wide range of taxa, similar studies in males have been scarce. Here, we examined geographic variation in male testis mass of the brown frog (Rana kukunoris) across seven different altitudes on the eastern Tibetan plateau, and tested the hypothesis that relative size of testis mass should increase with increasing temperature and/or decreasing seasonality. In this study, we found male body condition, age and testis mass did not increase with temperature and temperature seasonality, which do not conform to our previous hypothesis, revealing that differences in temperature and temperature seasonality across populations could not drive the evolution of testis size. However, we found a positive correlation between testis mass and body condition or age when controlling for population and the effect of temperature and temperature seasonality, indicative of a condition-dependent expression of testis size. In addition, a correlation between testis mass and operational sex ratio was not significant, suggesting that male–male competition did not lead to increasing levels of sperm competition.

Human pathogenic RNA viruses establish noncompeting lineages by occupying independent niches

Many pathogenic viruses are endemic among human populations and can cause a broad variety of diseases, some potentially leading to devastating pandemics. How virus populations maintain diversity and what selective pressures drive population turnover is not thoroughly understood. We conducted a large-scale phylodynamic analysis of 27 human pathogenic RNA viruses spanning diverse life history traits, in search of unifying trends that shape virus evolution. For most virus species, we identify multiple, cocirculating lineages with low turnover rates. These lineages appear to be largely noncompeting and likely occupy semiindependent epidemiological niches that are not regionally or seasonally defined. Typically, intralineage mutational signatures are similar to interlineage signatures. The principal exception are members of the family Picornaviridae, for which mutations in capsid protein genes are primarily lineage defining. Interlineage turnover is slower than expected under a neutral model, whereas intralineage turnover is faster than the neutral expectation, further supporting the existence of independent niches. The persistence of virus lineages appears to stem from limited outbreaks within small communities, so that only a small fraction of the global susceptible population is infected at any time. As disparate communities become increasingly connected through globalization, interaction and competition between lineages might increase as well, which could result in changing selective pressures and increased diversification and/or pathogenicity. Thus, in addition to zoonotic events, ongoing surveillance of familiar, endemic viruses appears to merit global attention with respect to the prevention or mitigation of future pandemics.

Timescales modulate optimal lysis-lysogeny decision switches and near-term phage reproduction.

Temperate phage can initiate lysis or lysogeny after infecting a bacterial host. The genetic switch between lysis and lysogeny is mediated by phage regulatory genes as well as host and environmental factors. Recently, a new class of decision switches was identified in phage of the SPbeta group, mediated by the extracellular release of small, phage-encoded peptides termed arbitrium. Arbitrium peptides can be taken up by bacteria prior to infection, modulating the decision switch in the event of a subsequent phage infection. Increasing the concentration of arbitrium increases the chance that a phage infection will lead to lysogeny, rather than lysis. Although prior work has centered on the molecular mechanisms of arbitrium-induced switching, here we focus on how selective pressures impact the benefits of plasticity in switching responses. In this work, we examine the possible advantages of near-term adaptation of communication-based decision switches used by the SPbeta-like group. We combine a nonlinear population model with a control-theoretic approach to evaluate the relationship between a putative phage reaction norm (i.e. the probability of lysogeny as a function of arbitrium) and the extent of phage reproduction at a near-term time horizon. We measure phage reproduction in terms of a cellular-level metric previously shown to enable comparisons of near-term phage fitness across a continuum from lysis to latency. We show the adaptive potential of communication-based lysis–lysogeny responses and find that optimal switching between lysis and lysogeny increases the near-term phage reproduction compared to fixed responses, further supporting both molecular- and model-based analyses of the putative benefits of this class of decision switches. We further find that plastic responses are robust to the inclusion of cellular-level stochasticity, variation in life history traits, and variation in resource availability. These findings provide further support to explore the long-term evolution of plastic decision systems mediated by extracellular decision-signaling molecules and the feedback between phage reaction norms and ecological context.

Compensating for Small Body Size: The Reproductive Ecology of Southern Spotted Turtle (Clemmys guttata) Populations

Gradients in environmental conditions across a species' geographic distribution can drive variability in a variety of life history traits. In North American freshwater turtles, both body and clutch size have commonly been shown to vary latitudinally, and these two traits are often directly related, with larger individuals producing larger clutches. We studied the reproductive ecology in two Georgia populations of Spotted Turtles (Clemmys guttata) from 2016–2020 by attaching radio transmitters to female turtles during the breeding season. We x-rayed turtles to determine clutch sizes and used thread bobbins to locate nesting locations, allowing us to determine nest fates. Across all Spotted Turtle clutches (n = 41), mean clutch size was 2.1 (range: 1–4) eggs per clutch. Approximately 92% of individuals that we monitored produced at least one clutch during the breeding season, and we identified 16 instances of individuals producing more than one clutch in a single year, including six turtles triple clutching during 2018. We located 24 Spotted Turtle nests during the study, nine (37.5%) of which either hatched or partially hatched. The other nests were either depredated (41.7%), did not hatch due to infertility or environmental reasons (8.3%), or had an undetermined fate (12.5%). Our results indicate that annual reproductive output in southern Spotted Turtle populations can exceed that of northern populations where individuals produce a single larger clutch per reproductive season. Finally, opportunistic observations in Florida from 2014–2021 indicated that the reproductive season can begin over a month earlier than in southern Georgia, highlighting the variability in reproductive ecology even across a relatively short latitudinal distance.

Effects of stem rotifer body size on morphology, starvation resistance and population growth of offspring in Brachionus calyciflorus

The morphological plasticity of rotifers has been investigated for several decades, and the maternal effects as an important source of variation in life history traits of rotifers have been reported. However, little is known in relation to the effects of maternal body size on offspring. In the represent study, resting eggs were collected from three Brachionus calyciflorus strains (A, B and C). From the hatchlings of each strain, the biggest and smallest stem rotifers were collected and named as the large-sized and small-sized morphotypes, respectively. The differences in body size (at 20 °C, 25 °C and 30 °C), starvation resistance and population growth were compared between strains and morphotypes. The results showed that strain and morphotype of maternal rotifers showed more important effects on the body size of offspring than temperature. Large-sized stem rotifers revealed significantly bigger offspring than small-sized stem rotifers, indicating significant maternal effects of body size on the morphology of offspring. At 25 °C, compared with small-sized stem rotifers, the offspring of large-sized stem rotifers showed significantly longer starvation resistance time in strain C and significantly higher population growth rate in strain B. These results demonstrated that strain is an important factor affecting the maternal effects of stem rotifer body size on offspring. Overall, this study provides more information to understand the morphological diversity of rotifers in field environments.

The Island of Female Power? Intersexual Dominance Relationships in the Lemurs of Madagascar

The extant primates of Madagascar (Lemuriformes) represent the endpoints of an adaptive radiation following a single colonization event more than 50 million years ago. They have since evolved a diversity of life history traits, ecological adaptations and social systems that rivals that of all other living primates combined. Their social systems are characterized by a unique combination of traits, including the ability of adult females to dominate adult males. In fact, there is no other group of mammals in which female dominance is so widespread. Yet, recent research has indicated that there is more interspecific variation in lemur intersexual relationships than previously acknowledged. Here, we therefore review and summarize the relevant literature, quantifying the extent of sex-bias in intersexual dominance relations documented in observational and experimental studies in captivity and the wild. Female dominance is often, but not always, implemented by spontaneous male submission in the absence of female aggression and linked to female sexual maturation. We connect the available evidence to the hypotheses that have been proposed to explain the evolution of female dominance among lemurs. The occurrence of female dominance in all lemur families and the interspecific variation in its extent indicate that it has evolved soon after lemurs colonized Madagascar – presumably in response to particular ecological challenges – and that it has since been reduced in magnitude independently in some taxa. Our study contributes important comparative information on sex roles from an independent primate radiation and provides general insights into the conditions, opportunities and obstacles in the evolution of female-biased power.

Diversity of life history traits, growth, and lipid storage in migratory variants of steelhead and rainbow trout (Oncorhynchus mykiss) in Kamchatka, Russia

Partial migration in salmonids provides access to freshwater and marine feeding environments varying in productivity. To test the hypothesis that partial migration drives differences in growth and energy storage with differential consequences for females than males, we assigned Oncorhynchus mykiss sampled on the western Kamchatka Peninsula, Russia, to one of five life history contingents based on scale patterns. Stable isotopes, obtained from a subset of fish, indicated different foraging by fish showing oceanic and coastal anadromous life histories. In younger fish, body size was largest in anadromous fish feeding on the high seas, intermediate for those feeding in coastal environments, and smallest for nonanadromous fish feeding in rivers. Older fish converged on large (oceanic) and small (coastal and freshwater) body sizes. Somatic lipid content, also collected for a subset of fish, averaged 2.5% across all life histories. Percent lipid was highest in females of ocean and males of coastal and freshwater life histories. Taken together, migratory patterns predictably influenced growth but may limit compensatory lipid storage in females, especially for the rare life histories.

Variation in abundance and life-history traits of two congeneric Arctic wolf spider species, Pardosa hyperborea and Pardosa furcifera, along local environmental gradients

The Arctic tundra is characterised by harsh conditions and environmental gradients are especially pronounced. Variation in functional traits along such gradients provide insights into the drivers of species abundance and distribution and are particularly valuable in this region currently experiencing strong climate warming. Over three consecutive years, we analysed the interacting effect of two environmental factors, habitat and elevation, on the abundance, body size, and clutch size in two common Low-Arctic invertebrate predators (Lycosidae, Araneae), Pardosa furcifera (Thorell 1875) and Pardosa hyperborea (Thorell 1872). Using generalised linear models, we firstly showed a habitat partitioning between P. furcifera, which dominated wet habitats, like fens, and P. hyperborea, which was more associated with drier habitats, like shrubs. Secondly, we found smaller body sizes at high elevation in P. hyperborea, a species that has a southern distribution in Greenland, and we identified season length as a major driver of the development in this species. In P. furcifera, a species likely more cold adapted, we found no body size difference between elevations, suggesting that local conditions (e.g. prey availability or snowmelt timing) are more important in explaining body size variations. Finally, body size and clutch size were strongly correlated in both species, but clutch size was not affected by habitat or elevation. We argue that fecundity is likely influenced by trade-offs and that considering additional complementary trait measurements would allow for a better understanding of the mechanisms underlying patterns in species life-history traits along environmental gradients.

Cooperation by necessity: condition- and density-dependent reproductive tactics of female house mice

Optimal reproductive strategies evolve from the interplay between an individual’s intrinsic state and extrinsic environment, both factors that are rarely fixed over its lifetime. Conditional breeding tactics might be one evolutionary trajectory allowing individuals to maximize fitness. We apply multi-state capture-mark-recapture analysis to a detailed 8-year data set of free-ranging house mice in a growing population to discern causes and fitness consequences of two alternative reproductive tactics in females, communal and solitary breeding. This allows us to integrate natural variation in life-history traits when analysing the expression of two alternative reproductive tactics in females. We find that communal breeding reduces average population fitness, but nevertheless increases over our 8-year study period. The tactic proves to be expressed conditionally dependent on both population density and female body mass – allowing females to breed under subpar conditions, i.e. at high density or when of low body mass. Our results contradict previous laboratory studies and emphasize the importance of studying cooperation under natural conditions, including natural variation in state-dependent survival and breeding probabilities.

Effects of a Bulking Agent on the Protein:Carbohydrate Ratio, Bioconversion, and Cost-effectiveness of a Larval Diet for Anastrepha ludens (Diptera: Tephritidae).

Although the bulking agent is categorized as 'inert', it could modify protein bioavailability and nutritional quality. In this study, the main goal was to determine if the bulking agent modified the protein:carbohydrate (P:C) ratio and bioconversion from diet biomass to larval biomass of Anastrepha ludens. The diet was altered only by modifying the type of bulking agent (corncob powder, coconut fiber, carrot fiber, oatmeal) added without changing the composition and concentration of the other components in the formulation. This allowed reclassification of the food matrices according to P:C ratios of 1:30, 1:35, 1:64, and 1:93. A food matrix with a high P:C ratio promoted a high protein and carbohydrate content in the larval hemolymph and immediately influenced the life-history traits of the larva or delayed them in the adult. The present study indicated a positive relationship between the P:G+T (glucose+trehalose) ratio in the larval hemolymph and the P:C ratio in the larval diet. Our results highlight the importance of including the optimum and real P:C ratio in whole fresh larval diets, since considering only the theoretical concentration of the formulation is not enough to understand the variation in key life-history traits. In addition, the bioconversion index should be included as an indicator of the efficacy of larval diets for mass rearing insects. A diet with high cost-effectiveness should be evaluated by taking into account flying flies as the end product of the mass rearing process to enhance operational SIT programs.

Divergence in life-history traits among three adjoining populations of the sea snake Emydocephalus annulatus (Hydrophiinae, Elapidae)

Life-history traits such as rates of growth, survival and reproduction can vary though time within a single population, or through space among populations, due to abiotically-driven changes in resource availability. In terrestrial reptiles, parameters such as temperature and rainfall generate variation in life-histories—but other parameters likely are more important in marine systems. We studied three populations of sea snakes (Emydocephalus annulatus) in adjacent bays in the IndoPacific archipelago of New Caledonia. The extreme philopatry of individual snakes allows us to unambiguously allocate each animal to one of the three populations. Although water temperatures and rainfall do not differ over this small scale, one site experiences more intense winds, restricting opportunities for foraging. Our 18-year mark-recapture dataset (> 1,200 snakes, > 2,400 captures) reveals significant divergence among populations in life-history traits. Survival rates and population densities were similar among sites, but snakes at the most wind-exposed site (Anse Vata) exhibited lower body condition, slower growth, less frequent production of litters, and smaller litters. Weather-driven variation in feeding rates thus may affect life-history traits of marine snakes as well as their terrestrial counterparts, but driven by different parameters (e.g., wind exposure rather than variation in temperatures or rainfall).

Feather growth and quality across passerines is explained by breeding rather than moulting latitude.

Tropical bird species are characterized by a comparatively slow pace of life, being predictably different from their temperate zone counterparts in their investments in growth, survival and reproduction. In birds, the development of functional plumage is often considered energetically demanding investment, with consequences on individual fitness and survival. However, current knowledge of interspecific variation in feather growth patterns is mostly based on species of the northern temperate zone. We evaluated patterns in tail feather growth rates (FGR) and feather quality (stress-induced fault bar occurrence; FBO), using 1518 individuals of 167 species and 39 passerine families inhabiting Afrotropical and northern temperate zones. We detected a clear difference in feather traits between species breeding in the temperate and tropical zones, with the latter having significantly slower FGR and three times higher FBO. Moreover, trans-Saharan latitudinal migrants resembled temperate zone residents in that they exhibited a comparatively fast FGR and low FBO, despite sharing moulting environments with tropical species. Our results reveal convergent latitudinal shifts in feather growth investments (latitudinal syndrome) across unrelated passerine families and underscore the importance of breeding latitude in determining cross-species variation in key avian life-history traits.

Postnatal expression of IGF2 is the norm in amniote vertebrates.

The insulin and insulin-like signalling (IIS) network plays an important role in mediating several life-history traits, including growth, reproduction and senescence. Although insulin-like growth factors (IGFs) 1 and 2 are both key hormones in the vertebrate IIS network, research on IGF2 in juveniles and adults has been largely neglected because early biomedical research on rodents found negligible IGF2 postnatal expression. Here, we challenge this assumption and ask to what degree IGF2 is expressed during postnatal life across amniotes by quantifying the relative gene expression of IGF1 and IGF2 using publicly available RNAseq data for 82 amniote species and quantitative polymerase chain reaction on liver cDNA at embryonic, juvenile and adult stages for two lizard, bird and mouse species. We found that (i) IGF2 is expressed postnatally across amniote species and life stages-often at a higher relative expression than IGF1, contradicting rodent models; (ii) the lack of rodent postnatal IGF2 expression is due to phylogenetic placement, not inbreeding or artificial selection; and (iii) adult IGF2 expression is sex-biased in some species. Our results demonstrate that IGF2 expression is typical for amniotes throughout life, suggesting that a comprehensive understanding of the mechanisms mediating variation in life-history traits will require studies that measure both IGFs.

Experimental Evolution in Tetrahymena.

Experimental evolution has provided novel insight into a wide array of biological processes. Species in the genus Tetrahymena are proving to be a highly useful system for studying a range of questions using experimental evolution. Their unusual genomic architecture, diversity of life history traits, importance as both predator and prey, and amenability to laboratory culture allow them to be studied in a variety of contexts. In this paper, we review what we are learning from experimental evolution with Tetrahymena about mutation, adaptation, and eco-evolutionary dynamics. We predict that future experimental evolution studies using Tetrahyemena will continue to shed new light on these processes.