Life-history evolution when Lestes damselflies invaded vernal ponds

We know little about the macroevolution of life-history traits along environmental gradients, especially with regard to the directionality compared to the ancestral states and the associated costs to other functions. Here we examine how age and size at maturity evolved when Lestes damselflies shifted from their ancestral temporary pond habitat (i.e., ponds that may dry once every decade or so) to extremely ephemeral vernal ponds (ponds that routinely dry completely each year). Larvae of three species were reared from eggs until emergence under different levels of photoperiod and transient starvation stress. Compared to the two temporary-pond Lestes, the phylogenetically derived vernal-pond Lestes dryas developed more rapidly across photoperiod treatments until the final instar, and only expressed plasticity in development time in the final instar under photoperiod levels that simulated a later hatching date. The documented change in development rate can be considered adaptive and underlies the success of the derived species in vernal ponds. Results suggest associated costs of faster development are lower mass at maturity and lower immune function after transient starvation stress. These costs may not only have impeded further evolution of the routine development rate to what is physiologically maximal, but also maintained some degree of plasticity to time constraints when the habitat shift occurred.     

Cannibalism-mediated life history plasticity to combined time and food stress

There is increasing awareness that combinations of biotic and time stress interact in shaping life history plasticity. Despite being widespread and abundant, the role of cannibalism in linking both types of constraints to life history plasticity has been largely neglected. Moreover, no studies disentangled direct (due to the extra meal) and indirect (due to the elimination of the competitor) life history effects of cannibalism, and little is known about their differential dependency on these constraints. We studied effects of cannibalism on the life history of the damselfly Lestes viridis under combinations of time stress (by manipulating the perceived time available in the growth season) and food stress. We reared larvae per two and disentangled direct and indirect effects of cannibalism by preventing cannibalism in half of the cups and by manipulating the per capita food increase after cannibalism. Cannibalism was more frequent under both time stress and food stress and our results show it may help cannibals to compensate for the negative effects of these constraints imposed on life history. Both direct and indirect benefits of cannibalism (increased development and growth rates, larger mass at emergence) were dependent on the timing of cannibalism, being more pronounced or only present when cannibalism occurred early. Moreover, we found that the ecological constraints (time stress and food stress) also differentially shaped some of the direct and indirect effects. Given the differential context-dependency of direct and indirect effects and the fact that direct and indirect life history effects may be both important in shaping life history, disentangling these effects is critical to mechanistically understand under which conditions cannibalism is expected to be adaptive or not.     

Life history comparisons of Daphnia obtusa from temporary ponds, cultured with a low-quality food

Temporary pond Daphnia flourish on relatively poor-quality food, suggesting adaptation to stringent temporary pond conditions. We conducted laboratory life history experiments on populations of Daphnia obtusa from a shaded woodland temporary pond (short hydroperiod, dystrophic) and an open farmland temporary pond (long hydroperiod, eutrophic), and compared a suite of physical/chemical conditions in the ponds to evaluate habitat conditions. We hypothesized that the shaded woodland pond population would be more fit in terms of life history variables for individuals (age and size at first reproduction, mean brood size, mean number of neonates) and populations (generation time, net reproductive rate R ₀, and intrinsic reproductive rate r) given a standard, low-quality food (trout chow and yeast). Life history traits of woodland pond animals were mixed, relative to farm pond animals, and consistent with bet-hedging for an unpredictable habitat. Values of life history traits rivaled or exceeded those of other studies using phytoplankton as food, and were influenced by the pond water used for our study. Life histories clearly differ among local and regional temporary pond Daphnia obtusa populations, and should be valuable for examining the relative influences of local selection and metapopulation dynamics on population structure.     

Microgeographic life history variation in an alpine caddisfly: plasticity in response to seasonal time constraints

1. Temporally constrained environments, such as habitats with short growth seasons or short hydroperiods, cause potentially strong selection on life histories. Depending on the predictability of these events and the extent of spatial and temporal heterogeneity, local populations could become adapted either via a fixed phenotype or via life history plasticity in response to these environmental cues. 2. We used a common garden experiment to investigate microgeographic variation in life history responses to combined changes in photoperiod (ambient/late) and hydroperiod (constant/drying) time constraint cues in an alpine caddisfly (Trichoptera). We compared six populations (three permanent/three temporary streams) originating from a small, alpine floodplain and which spanned an expected gradient in growth period duration (GPD) with distance from glaciers. 3. We made two main predictions in relation to locally varying selection pressures: (i) populations nearest glaciers (shorter GPD and strongest time constraints) should have the fastest development rates and (ii) populations from permanent streams should be less able to respond to drying hydroperiods than populations from temporary streams. 4. All populations and both sexes accelerated development in response to late season photoperiod cues. However, only permanent stream populations showed an increase in development time with increasing GPD, suggesting that other factors were influencing populations in temporary streams. 5. Permanent stream populations showed countergradient variation (genetic and environmental influences were in opposition) in development time, and under‐compensation of growth rates resulted in a converse Bergmann cline in body size (smaller body size along gradients of declining season length). The extent of plasticity in response to hydroperiod, and the combined effects of both time constraints, differed between populations and sexes, but were not consistent among populations. 6. Taken together, our results suggest adaptive plasticity in response to season length. The lack of a predictable pattern in response to hydroperiod may be due to gene flow or weak selection. We conclude that spatially structured populations can strongly differ in phenotypic plasticity even at microgeographic scales.     

Life history reaction norms to time constraints in a damselfly: differential effects on size and mass

Optimality models predict that, under a time constraint, organisms should accelerate development, and preferably so by increasing growth rate, to keep size at emergence constant. Unfortunately, most tests did neglect genetic constraints and interchanged mass with body size which may explain mixed support for some of the models' predictions. We imposed time constraints on full sibling larvae of the damselfly Enallagma cyathigerum by manipulating day length regimes. Under a time constraint, larval development and growth rate based on size indeed were faster. This made it possible to keep size at emergence constant, despite the shorter development time. Interestingly, under a time constraint, growth rate based on mass was not increased and larvae had a lower mass at emergence. We see two reasons for this difference between body mass and size. First, size is fixed at emergence, while mass can still increase in many insects. Secondly, genetic constraints may have contributed to different responses for size and mass. In general, our results strongly suggest discriminating between size and mass when testing life history responses.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 187–196.     

Life history plasticity and population regulation in sea otters

We contrasted body condition, and age‐specific reproduction and mortality between a growing population of sea otters (Enhydralutris) at Kodiak Island and a high‐density near‐equilibrium population at Amchitka Island, Alaska. We obtained data from marked individuals, population surveys, and collections of beach‐cast carcasses. Mass:length ratios indicated that females (but not males) captured in 1992 at Amchitka were in poorer condition than those captured at Kodiak in 1986–1987. In 1993, the condition of females at Amchitka improved in apparent response to two factors: (1) an episodic influx of Pacific smooth lumpsuckers, Aptocyclus ventricocus, from the epi‐pelagic zone, which otters consumed; and (2) an increase in the otters’ benthic invertebrate prey resulting from declining otter numbers. Reproductive rates varied with age (0.37 [CI=0.21 to 0.53] births female^?1 yr^?1 for 2–3‐yr‐olds, and 0.83 [CI=0.69 to 0.90] for females ≥4 yr old), and were similar at both areas. Weaning success (pups surviving to ≥120 d), in contrast, was almost 50% lower at Amchitka than at Kodiak and for females ≥4 yr of age was 0.52 (CI=0.38 to 0.66) vs 0.94 (CI=0.75 to 0.99), respectively. Sixty‐two percent of the preweaning pup losses at Amchitka occurred within a month of parturition and 79% within two months. Postweaning survival was also low at Amchitka as only 18% of instrumented pups were known to be alive one year after mother‐pup separation. Adult survival rates appeared similar at Amchitka and Kodiak. Factors affecting survival early in life thus are a primary demographic mechanism of population regulation in sea otters. By maintaining uniformly high reproductive rates over time and limiting investment in any particular reproductive event, sea otters can take advantage of unpredictable environmental changes favorable to pup survival. This strategy is consistent with predictions of “bet‐hedging” life history models.     

Digest: Life history evolution in Darwin's dream ponds*

Can variation in sex‐specific parental investment lead to sexual dimorphism in immune response? Keller et al. (2018) measured immune cell parameters, expression of candidate genes, and composition of buccal microbiota in mouthbrooding cichlid species from Lake Tanganyika that show either maternal or biparental care. They found that maternal mouthbrooding species have increased sexual dimorphism in immune parameters, while biparental mouthbrooders exhibit an upregulated adaptive immune response, suggesting resource allocation shifts between parental investment and the immune system.     

Effect of shade and shading history on species abundances and ecosystem processes in temporary ponds

1. The amount of sunlight that an ecosystem receives is an important determinant of primary productivity, which in turn can influence species diversity and nutrient cycling. Here, we examine the effects of shading and shading history on ecosystem processes, macroinvertebrate diversity and development of dominant ecosystem states in field‐based aquatic mesocosms. 2. We found that there were large effects of the level of shade, but few effects of shading history. Increasing light increased the biomass of filamentous algae (metaphyton) which increased the overall productivity of the ecosystem, and shifted the invertebrate community from one with more mosquitoes (filter feeders) to one with more anuran tadpoles (algal grazers). 3. There was also an effect of shading history, where increased shade led to changes in the macroinvertebrate communities that were maintained after shade was reduced in the later part of the experiment. 4. Finally, our results indicated that correlations between ecosystem processes, specific key macrofauna and the development of pond ecosystem states were greater than correlations of these factors to shading treatments. These results suggest that the history of community assembly can have a greater impact on the development of ecosystem processes than diminishing light by as much as 50%. However, light may have a potentially strong indirect effect and may impact the communities through altered bottom‐up structuring forces.     

Phenotypic plasticity in two marine snails: constraints superseding life history

In organisms encountering predictable environments, fixed development is expected, whereas in organisms that cannot predict their future environment, phenotypic plasticity would be optimal to increase local adaptation. To test this prediction we experimentally compared phenotypic plasticity in two rocky-shore snail species; Littorina saxatilis releasing miniature snails on the shore, and Littorina littorea releasing drifting larvae settling on various shores, expecting L. littorea to show more phenotypic plasticity than L. saxatilis. We compared magnitude and direction of vectors of phenotypic difference in juvenile shell traits after 3 months exposure to different stimuli simulating sheltered and crab-rich shores, or wave-exposed and crab-free shores. Both species showed similar direction and magnitude of vectors of phenotypic difference with minor differences only between ecotypes of the nondispersing species, indicating that plasticity is an evolving trait in L. saxatilis. The lack of a strong plastic response in L. littorea might be explained by limits rather than costs to plasticity.     

Life history plasticity and fitness in a caddisfly in response to proximate cues of pond-drying

The majority of plants are involved in symbioses with arbuscular mycorrhizal fungi (AMF), and these associations are known to have a strong influence on the performance of both plants and insect herbivores. Little is known about the impact of AMF on complex trophic chains, although such effects are conceivable. In a greenhouse study we examined the effects of two AMF species, Glomus intraradices and G. mosseae on trophic interactions between the grass Phleum pratense, the aphid Rhopalosiphum padi, and the parasitic wasp Aphidius rhopalosiphi. Inoculation with AMF in our study system generally enhanced plant biomass (+5.2%) and decreased aphid population growth (−47%), but there were no fungal species-specific effects. When plants were infested with G. intraradices, the rate of parasitism in aphids increased by 140% relative to the G. mosseae and control treatment. When plants were associated with AMF, the developmental time of the parasitoids decreased by 4.3% and weight at eclosion increased by 23.8%. There were no clear effects of AMF on the concentration of nitrogen and phosphorus in plant foliage. Our study demonstrates that the effects of AMF go beyond a simple amelioration of the plants’ nutritional status and involve rather more complex species-specific cascading effects of AMF in the food chain that have a strong impact not only on the performance of plants but also on higher trophic levels, such as herbivores and parasitoids.     

Phenotypic plasticity and optimal timing of metamorphosis under uncertain time constraints

Life-history theory suggests that optimal timing of metamorphosis should depend on growth conditions and time constraints under which individuals develop. Current models cannot make reliable predictions for species in ephemeral habitats where individuals often face an increasing mortality risk over time because these models assume time-invariant mortality rates (i.e., daily mortality rates remain constant) and fixed seasons. We examined the plasticity of growth, development, and body mass at metamorphosis in tadpoles of the tree-hole breeding frog Phrynobatrachus guineensis in relation to an unpredictable time constraint in the field and in controlled experiments along a fixed density and food gradient. Mean mass and age at metamorphosis of sibships were positively correlated with per capita food level. Based on our results, we developed a simple model of the optimal timing of metamorphosis under time-dependent mortality rates showing that development rates are not only adjusted to growth conditions but also to time-variant mortality rates. The increasing mortality rate represents a time constraint that favors a reduced larval period, but because it is based on probabilities of survival it allows a trade-off between development time and mass. We extend this model to different types of time constraints and show that it can predict the range of documented reaction norms. Differences between species in␣the correlation of age and mass at metamorphosis may have evolved due to differences in their time-variant mortality rates.     

Life history and development--a framework for understanding developmental plasticity in lower termites

Termites (Isoptera) are the phylogenetically oldest social insects, but in scientific research they have always stood in the shadow of the social Hymenoptera. Both groups of social insects evolved complex societies independently and hence, their different ancestry provided them with different life-history preadaptations for social evolution. Termites, the 'social cockroaches', have a hemimetabolous mode of development and both sexes are diploid, while the social Hymenoptera belong to the holometabolous insects and have a haplodiploid mode of sex determination. Despite this apparent disparity it is interesting to ask whether termites and social Hymenoptera share common principles in their individual and social ontogenies and how these are related to the evolution of their respective social life histories. Such a comparison has, however, been much hampered by the developmental complexity of the termite caste system, as well as by an idiosyncratic terminology, which makes it difficult for non-termitologists to access the literature.
Here, we provide a conceptual guide to termite terminology based on the highly flexible caste system of the "lower termites". We summarise what is known about ultimate causes and underlying proximate mechanisms in the evolution and maintenance of termite sociality, and we try to embed the results and their discussion into general evolutionary theory and developmental biology. Finally, we speculate about fundamental factors that might have facilitated the unique evolution of complex societies in a diploid hemimetabolous insect taxon. This review also aims at a better integration of termites into general discussions on evolutionary and developmental biology, and it shows that the ecology of termites and their astounding phenotypic plasticity have a large yet still little explored potential to provide insights into elementary evo-devo questions.     

Fish assemblages in temporary ponds adjacent to 'terra-firme' streams in Central Amazonia

1. The effect of habitat structural features and physicochemical characteristics of the water on the composition and richness of fish assemblages in temporary ponds near streams were examined at three spatial scales: among ponds, among streams and between drainage basins, in a ‘terra‐firme’ (not subject to long‐term flooding) forest reserve in Central Amazonia. 2. The fish assemblage in temporary ponds was composed of subsets of 18 small‐bodied species widely distributed in the reserve. The assemblages had a nested subset structure, where smaller ponds contained subgroups of the species found in larger ponds. 3. Species composition and richness in temporary ponds were similar between drainage basins, although the fish assemblages in streams differed between basins. 4. Fish assemblage structure was influenced by local factors related to habitat structure, such as pond area and depth, canopy cover and hydroperiod. Physicochemical characteristics of the water in the ponds were similar between drainage basins and had little detectable effect on the structure of pond fish assemblages. 5. No correspondence was found between the composition, richness or abundance of fishes in the ponds and in stretches of the streams adjacent to the ponds. Therefore, it is not possible to predict the composition of these temporary pond fish assemblages from the fish assemblages found in adjacent streams.     

Physical and chemical features of a vernal temporary pond in Western Canada

Temporal changes in physical and chemical features of a vernal temporary pond in western Canada are described for the 7-week duration of the pond. Average water loss through evaporation was 3 m³/day. Daily temperature ranges of 11 and 12° were frequent. Specific conductance, hardness and bicarbonate alkalinity increased progressively in proportion to the decrease in pond volume. Increase in chlorides was much less than predicted from evaporative concentration. Sulphates increased rapidly during the filling phase but then decreased steadily during the remaining weeks. The decline is attributed to uptake by meadow vegetation. Other biologically important ions examined exhibited no distinct patterns. The relative importance of evaporation, capillary creep and biological uptake processes is discussed.     

Life history evolution in Asobara tabida: plasticity in allocation of fat reserves to survival and reproduction

Life history variation can be genetically based, or it may be due to environmental effects on the phenotype. In this paper we examine life history variation in relation to differences in habitat in the parasitoid Asobara tabida. Differences in the spatial distribution of host patches, the length of the season, host suitability, and competition between parasitoids all contribute to the selection for differences in life history between strains from northern and southern Europe. Strains were compared with respect to the allocation between reproduction and survival in experimental environments that varied with regard to the availability of food or to the number of hosts offered per day. Upon emergence parasitoids originating from southern Europe have higher egg loads and smaller fat reserves than parasitoids originating from northern Europe. Parasitoids from both southern and northern Europe show plasticity in allocation: food shortage causes a decrease in egg production, and rich breeding opportunities an increase in egg production. This plasticity is greater in the northern strain. Fat reserves play a central role in the physiology of this allocation. Fat can be used for both reproduction and survival. There is no oosorption, so once fat is allocated to reproduction it can no longer be used for survival. Differences in plasticity in allocation can therefore be considered as differences in the timing of egg production.     

Larval cannibalism, time constraints, and adult fitness in caddisflies that inhabit temporary wetlands

The fitness of non-feeding adult insects depends on energy accumulated during the larval stage. Larvae of the caddisfly Asynarchus nigriculus primarily feed on plant detritus, but supplement their diet with animal material obtained through cannibalism. Habitat drying constrains development in many populations of this species, and we hypothesized that cannibalism should accelerate development to facilitate timely metamorphosis. We manipulated larval diets in a field experiment by supplementing detritus with animal material, and in a laboratory experiment by varying animal material and detritus quality (conditioned vs unconditioned). We measured the effects of dietary manipulation on larval and pupal growth and development, the timing of metamorphosis, and adult fitness correlates. The results of the laboratory experiment suggest that this species can metamorphose with a detritus-only diet, but development is extremely protracted. In the field experiment, individuals with animal material in their diet had higher larval survival, shorter larval and pupal development times, and earlier emergence dates (7–10 days), than those without a supplement. This delay in emergence should have important effects on survival in natural populations where the difference between desiccation and successful emergence can be only a few days. Dietary supplementation also affected adult body mass (30–40% increase), female fecundity (30% more eggs), and proportional allocation to different adult body parts. Our results are consistent with recent growth-development models that predict coupled (earlier emergence and larger adults) rather than tradeoff responses (earlier emergence and smaller adults) to pre-threshold manipulation of larval diets. Many detritivorous aquatic insects supplement their diets with animal material, and our data provide evidence that this supplementation can have strong effects on fitness. This type of dietary supplementation should be especially important for taxa that do not feed as adults, and in temporary habitats that impose time constraints on larval development.     

Differential responses of zooplankton assemblages to environmental variation in temporary and permanent ponds

Permanent and temporary wetlands in Mediterranean shrublands represent unique repositories of biodiversity, which are increasingly threatened by human-induced habitat loss. The zooplankton of a permanent (P1) and a temporary pond (T35) in the Natural Reserve of Castelporziano, a rare residual stretch of such a shrubland in Central Italy (Latium), was investigated to: (1) expand and deepen knowledge of these endangered freshwater habitats, which represent a crucial component of Mediterranean biodiversity; (2) identify environmental controls regulating the development of zooplankton communities of each environment; and (3) highlight differences in the adaptive responses of the zooplankton community in relation to the different ecological conditions experienced by permanent and temporary habitats. Despite summer desiccation in T35, the two ponds exhibited a relative homogeneity in hydrological and physico-chemical dynamics. Zooplankton assemblages contained 41 total taxa, of which 32 were found in P1 and 28 in T35. Out of the 41 taxa identified, 22 (>50%) were exclusively present in one of the two ponds. On a yearly basis, the community dynamics of P1 seemed to be conditioned by physical and chemical factors and by hydrological cycle characteristics, while the community of T35 responded to algal blooms, food competition and predator/prey equilibria rather than correlating to abiotic factors. The main differences amongst zooplankton assemblages were observed over short time scales and occurred both within and between seasons, highlighting the role of some structural taxa that dominated the average composition of the community throughout the year, and the importance of “quick-response” taxa in determining the short-term composition and structure variation of pond zooplankton. A year-round cyclic community succession peculiar to each pond is described.     

Life history and morphological plasticity of the soybean aphid,Aphis glycines

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a pest of soybean, Glycine max (L.) Merr. (Fabaceae), from eastern Asia that was first reported in North America in 2000. The influence of temperature on plasticity of life history and morphological traits of the soybean aphid has not been tested despite observable differences in population growth and morphology among isolates in laboratory colonies. Therefore, we used three isolates of the aphid to test whether lifespan, growth rate, fecundity, and morphology were plastic at 16, 24, and 28 °C. Population size of the aphid was influenced by temperature, probably because two reproductive traits, maximum number of offspring in 1 day and total fecundity, were plastic and increased in successive generations at 24 °C. All morphological traits were plastic, including lengths of body parts, number of antennal segments and caudal hairs, and color of siphunculi and body, and they were differentially influenced by isolate and temperature. Knowledge about the life history and morphology of the soybean aphid may help identify its capacity for phenotypic plasticity in heterogeneous temperatures and identify how temperature influences its survival, population growth, and diversity.     

Life syndrome of the bryophyte communities as an adaptative pattern in the Mediterranean temporary ponds of Italy

An ecological and biological investigation on the bryophyte communities of the Mediterranean temporary ponds was carried out in Italy. Here, the occurrence of a rich set of liverworts is very significant, as several species of Riccia characterize the communities from a physiognomical, ecological and syntaxonomical point of view. The moss component is represented only by acrocarpous mosses, e.g. Archidium alternifolium and Pleuridium acuminatum which play an important phytosociological role. In this study, the bryophyte communities are used to identify a pattern, corresponding to a “functional type” which reflects the correlated response of the bryophyte communities toward the prevalent ecological parameters of the habitat. The individuated functional type assembles life strategy, life form, lifespan, spore size, dispersal strategy, reproduction effort, independently from the taxonomical relationship of the species characterizing the communities. It represents an adaptative pattern of coevolved characters, adopted by the bryophyte communities for the habitat establishment and re-establishment following the seasonal water fluctuations typical of the investigated habitat.     

Crustacean zooplankton community structure in temporary and permanent grassland ponds

Lentic community structure varies across a size gradient of ponds and lakes with physical factors, such as pond drying, and biotic factors, such as fish predation, determining the species assemblage. We studied the effects of pond drying and fish absence on crustacean zooplankton across a gradient of pond sizes in a Texas grassland. We determined the species compositions and size distributions of crustacean zooplankton in 20 temporary and 18 permanent ponds in April after March rains had refilled the ponds. The surface areas of temporary and permanent ponds ranged from <0.01 to 0.21 ha and 0.04 to 13.8 ha, respectively, and temporary ponds were significantly smaller, on average, than permanent ponds. Fish were absent from all temporary ponds and present in all permanent ponds. We detected a difference in the zooplankton species assemblages of the temporary and permanent ponds. Out of 14 total zooplankton taxa that occurred in eight or more ponds, seven taxa were significantly more prevalent in temporary ponds and four taxa were significantly more prevalent in permanent ponds. The sizes of zooplankton in the temporary fishless ponds were greater than those in the permanent ponds with fish present. We concluded that pond size mediated susceptibility to pond drying, and pond drying determined the presence and absence of fish and their secondary trophic-level effect on zooplankton community structure. Handling editor: Steven Declerck