Compared Life History Traits Research Articles

Greater costs of inducible behavioural defences at cooler temperatures in larvae of the mosquito, Aedes notoscriptus

The evolutionary maintenance of inducible defences is governed by the costs and benefits of the defensive traits. The defensive traits should increase the chances of survival in the presence of predators, but be costly in their absence. The costs and benefits of inducible defensive traits can be influenced by environmental conditions, which subsequently affect the ability of prey to induce those defensive traits. We examine how temperature affects the costs of behavioural defences in larval mosquitoes, Aedes notoscriptus, which reduce activity in the presence of predator cues to limit detectability. The costs of reducing activity could either be exacerbated at warmer temperatures via increased metabolic demand, or ameliorated at warmer temperatures via accelerated development reducing exposure time. We compared life history traits of A. notoscriptus reared in control conditions to those exposed to predation cues as larvae at 18, 23 and 28 °C. Larvae reared in predation cues reduced activity, grew and developed slower and emerged later and smaller. While the reduction in activity increased with temperature, the negative effects on life history of A. notoscriptus were greatest at the coolest temperature. Our results show that the costs of inducible defences in A. notoscriptus are temperature dependent. This work suggests that variation in the thermal environment may have a strong influence on the dynamics of predator–prey interactions and the evolutionary maintenance of plasticity of defensive traits in natural populations.

Estimating direct resistance in willows against a major insect pest, Phratora vulgatissima, by comparing life history traits

AbstractMany Salix species (Salicaceae) have a high energy quotum and efficient nitrogen use, resulting in a high and stable biomass production, making these plants suitable as bioenergy crops. However, Salix coppices are sensitive to herbivory by chrysomelid beetles, such as Phratora vulgatissima L. (Coleoptera: Chrysomelidae), and to maintain high biomass yields over several years, durable plant resistance is necessary. We have developed a reliable and efficient bioassay that can be used as a tool for detection of resistance against P. vulgatissima in Salix. Screening of six clones of one susceptible (Salix viminalis L.) and one resistant (Salix dasyclados Wimm.) willow species, by the response of several life history traits of larval and adult P. vulgatissima, identified egg production as the most reliable trait for resistance. We show that a 2‐week bioassay of oviposition rate is sufficient for a trustworthy estimation of both total egg production and survival of adult leaf beetles. In addition, to elucidate the variation in resistance among the studied clones, leaf concentrations of various phenolic compounds were compared with the key life history traits of the beetles. Phenolic compounds, especially salicylates, have previously been reported as the main factor controlling Salix resistance against P. vulgatissima. Indeed we found higher levels of salicylates in the resistant clones and larval performance was negatively correlated to the concentration of salicylates in the leaves. In addition, we found indications of negative effects of a luteolin derivative and quercetin‐3‐glucoside on leaf beetle performance, but further studies are needed to elucidate the specific roles that the different phenolic compounds play in plant resistance.

Same old Salmo? Changes in life history and demographic trends of North Iberian salmonids since the Upper Palaeolithic as revealed by archaeological remains and beast analyses

Life history traits determine fitness and hence the ability of populations and species to survive through adverse conditions. Therefore, identifying temporal changes in life history traits over large timescales is necessary to understand and predict the effect of current global change on wild populations. In this study, we compare life history traits between Palaeolithic and present-day vertebrates, analysing the number of winters spent in the river and at sea by North Iberian salmonids (Salmo salar and Salmo trutta) from two separate time frames: the Upper Palaeolithic, based on archaeological remains, and the present day, based on sport catches. The river stage did not change significantly, but the marine period has been shortened in modern anadromous specimens, accordingly shortening mean generation time. Population growth rates have been estimated through Bayesian analyses of the mitochondrial DNA control region of modern specimens for the two Salmo species using two different mutation rates (1% and 3.6%). Coincidence of coalescent N(e) estimates with independent N(e) calculated from catches suggests that the 3.6% mutation rate fits better the evolution of the studied populations. Population growth rate declines would have occurred in the last millennium and could be explained by a combination of climatic events and anthropogenic activities.

Rapid evolution of parasite life history traits on an expanding range‐edge

Parasites of invading species undergoing range advance may be exposed to powerful new selective forces. Low host density in range-edge populations hampers parasite transmission, requiring the parasite to survive longer periods in the external environment before encountering a potential host. These conditions should favour evolutionary shifts in offspring size to maximise parasite transmission. We conducted a common-garden experiment to compare life history traits among seven populations of the nematode lungworm (Rhabdias pseudosphaerocephala) spanning from the parasite population core to the expanding range-edge in invasive cane toads (Rhinella marina) in tropical Australia. Compared to conspecifics from the population core, nematodes from the range-edge exhibited larger eggs, larger free-living adults and larger infective larvae, and reduced age at maturity in parasitic adults. These results support a priori predictions regarding adaptive changes in offspring size as a function of invasion history, and suggest that parasite life history traits can evolve rapidly in response to the selective forces exerted by a biological invasion.

Living with the enemy: parasites and pathogens of the ladybird Harmonia axyridis

Harmonia axyridis is an invasive alien predator in many countries across the world. The rapid establishment and spread of this species is of concern because of the threat it poses to biodiversity as a generalist predator. Understanding the mechanisms that contribute to the success of this species as an invader is not only intriguing but also critical to our understanding of the processes governing such invasions. The enemy release hypothesis (ERH) could explain the rapid population growth of many invasive alien species. However, empirical evidence in support of the ERH is lacking. An alternative hypothesis that could explain rapid population growth is evolution of increased competitive ability (EICA). Here we provide an overview of the parasites and pathogens of coccinellids with a particular focus on H. axyridis as a host. We examine the differential susceptibility of host species and highlight the resilience of H. axyridis in comparison to other coccinellids. We recognise the paucity and limitations of available information and suggest that studies, within a life-table framework, comparing life history traits of H. axyridis in both the native and introduced ranges are necessary. We predict that H. axyridis could benefit from both enemy release and EICA within the introduced range but require further empirical evidence.

Many Possible Worlds: Expanding the Ecological Scenarios in Experimental Evolution

Experimental microbial evolution has focused on the particular ecological scenario where a population is placed suddenly in an environment where its fitness is low, and then adapts while the environment remains stable. In line with this, most microbial evolution studies use fitness measures that report how evolved genotypes fare when competed directly against their own distant ancestor while other studies compare life history traits (such as growth rates) of ancestral and evolved genotypes. This standard way of measuring and reporting changes in fitness has resulted in a consistent body of literature that explains adaptation when populations evolve in this “standard ecological scenario.” Here, I suggest that for experimental evolution to investigate adaptation in other ecological scenarios, such as fluctuating or persistently changing environments, measures of fitness must be expanded such that they not only continue to be comparable between experiments, but also account for evolution and demographic effects in all environments that an evolving lineage experiences. I examine two non-standard measures of fitness—fitness flux and the total number of reproductive events—as potential ways to quantify adaptation by integrating historical information about selection over many environments. This approach could allow us to make quantitative and biologically-meaningful comparisons of adaptation across diverse ecological scenarios. I use the case study of understanding how phytoplankton communities may respond to global change, where environmental variables change continuously, to explore concrete ways of using non-standard fitness measures that consider both demographic effects and selection in changing, rather than in changed, environments.

Comparative life-history traits of three phytoseiid mites associated with Tetranychus urticae (Acari: Tetranychidae) colonies in clementine orchards in eastern Spain: implications for biological control

The management of Tetranychus urticae, a key pest of clementine trees, is mainly based on the use of acaricides. However, more environmentally safe measures, such as biological control, are being encouraged. Life-history traits of the three most abundant phytoseiid mites associated with T. urticae on this crop (Euseius stipulatus, Phytoseiulus persimilis and Neoseiulus californicus) were studied. The experiments were performed under laboratory conditions (25 degrees C, 80 +/- 5% RH and 16:8 h (L:D)) on clementine leaves and T. urticae as prey. Euseius stipulatus could not complete its life cycle, whereas P. persimilis and N. californicus completed it satisfactorily. The estimated intrinsic rate of increase (rm) was significantly higher for P. persimilis (0.344 day(-1)) than for N. californicus (0.244 day(-1)) and both were higher than the rm value of T. urticae on clementine leaves. Implications of these results for the biological control of T. urticae in this crop are discussed.

Interactions between the direct and indirect effects of predators determine life history evolution in a killifish

The ecological impacts of the indirect effects of predators are well established, but the evolutionary consequences are unknown. Predators often decrease prey density, which indirectly increases the resources available to surviving prey. This ecological effect could provide a link to evolution because it is generally assumed that resource availability influences life history evolution. Yet, predictions from theory that consider food availability are inconsistent, and evidence for an important role of resources in shaping life history evolution is absent. We compared life history traits in a Trinidadian killifish, Rivulus hartii, from fish communities that differ in predation intensity; predators are associated with lower population density and faster growth rates. To determine whether the indirect effects of predators influence evolutionary change, we reared second-generation-born fish under two food levels that approximated natural differences in resources between communities. Rivulus from sites with predators are younger and smaller at maturity. They have increased reproductive investment and produce many small eggs and smaller hatchlings. Such divergence is predicted as a direct effect of predation. We also found significant interactions between predator community and food level for age and size at maturity, fecundity, and egg size. These interactions, whereby the differences between communities were more pronounced at high-food levels, argue that evolution in Rivulus has been influenced by the indirect effects of predators mediated through resource availability. Rivulus from sites with predators better exploit the higher resources in those habitats. Therefore, both direct and indirect effects of predators have evolutionary consequences.

Crayfish assemblage shifts in a large drought‐prone wetland: the roles of hydrology and competition

Summary1. Faster growing, larger and/or more aggressive crayfish species are predicted to dominate permanent waterbodies. We tested this prediction using a 9 year dataset for two species of crayfish (Procambarus alleni and Procambarus fallax) co‐existing in a sub‐tropical flowing slough in southern Florida. Using a series of laboratory and mesocosm experiments we also compared life history traits and performance of the respective species to test mechanisms that could explain dominance shifts in the local crayfish assemblages.2. Over the 9‐year period, P. alleni densities were the greatest in shallower, shorter‐hydroperiod areas bordering the slough, while P. fallax densities were higher in deeper, longer‐hydroperiod central areas. These areas were separated by 0.8–2 km of continuous wetland with no apparent barriers to movement between them.3. Density of P. fallax was not strongly affected by any measures of hydrological variation, while P. alleni density increased with more severe drought conditions. Following the strongest droughts, P. alleni colonized areas in the centre of the slough where they had been absent or scarce in wetter years.4. We conducted experiments to compare growth rates, drought tolerance, and competitive dominance of these species. P. alleni survived drought conditions better, had higher growth rates, and was the dominant competitor for space and food. While drought probably limits P. fallax in the drier slough habitats, neither drought sensitivity nor interspecific competition with P. fallax can explain decreases of P. alleni with wetter conditions.5. Our results indicate that a competition‐colonization tradeoff cannot explain the crayfish compositional dynamics in this wetland because P. alleni is both the best competitor and the best at surviving in and colonizing areas with the strongest droughts. Future attention should focus on the potential for selective effects of predators that co‐vary with hydrology.6. The traits (large size, fast growth, competitive dominance) exhibited by P. alleni, which is absent in long‐hydroperiod wetlands, are those exhibited by dominant crayfish in permanent lakes and streams containing fish. Although these traits make crayfish less vulnerable to fish in some lakes and streams, life‐history models of community structure across permanence gradients suggest the opposite traits should be favoured for co‐existence with fish.

Nematodes in wastewater biofilms—Appearance and density of species in three biofilter reactors

Population dynamics of nematode species in biofilms of three different biofilter reactors, differing in size (pilot/laboratory scale), operation mode and biofilm carrier, were studied over a period of 1 year. In the biofilm suspension of the pilot system mean nematode density was 118 individuals/ml and average biomass 15 μg wet weight/ml. Higher mean abundance was found in the two laboratory systems with 2380 and 4411 individuals/ml. Mean biomass in the laboratory systems ranged from 209 to 330 μg wet weight/ml. There were marked temporal differences in appearance and density of nematode species in all three biofilters. Number of species observed was 3 in the laboratory systems and 5 in the pilot system. The fastest growing species ( Paroigolaimella bernensis and Diplogasteritus nudicapitatus) were observed in the pilot reactor in contrast to the more slowly growing species ( Diploscapter coronatus and Acrostichus sp.), which dominated in the laboratory reactors. Sexual reproduction was found for all species but of Diploscapter coronatus. When comparing life history traits of the different species with the environmental conditions in the reactors, it seems that the unstable conditions in the pilot reactor favor the fast growing species whereas the stable environment in the laboratory systems allows the growth of species with longer generation times.

Viruses' Life History: Towards a Mechanistic Basis of a Trade-Off between Survival and Reproduction among Phages

Life history theory accounts for variations in many traits involved in the reproduction and survival of living organisms, by determining the constraints leading to trade-offs among these different traits. The main life history traits of phages—viruses that infect bacteria—are the multiplication rate in the host, the survivorship of virions in the external environment, and their mode of transmission. By comparing life history traits of 16 phages infecting the bacteria Escherichia coli, we show that their mortality rate is constant with time and negatively correlated to their multiplication rate in the bacterial host. Even though these viruses do not age, this result is in line with the trade-off between survival and reproduction previously observed in numerous aging organisms. Furthermore, a multiple regression shows that the combined effects of two physical parameters, namely, the capsid thickness and the density of the packaged genome, account for 82% of the variation in the mortality rate. The correlations between life history traits and physical characteristics of virions may provide a mechanistic explanation of this trade-off. The fact that this trade-off is present in this very simple biological situation suggests that it might be a fundamental property of evolving entities produced under constraints. Moreover, such a positive correlation between mortality and multiplication reveals an underexplored trade-off in host–parasite interactions.

Effects of Cotton Cultivar on Fitness Costs Associated with Resistance of Pink Bollworm (Lepidoptera: Gelechiidae) to Bt Cotton

Fitness costs associated with insect resistance to transgenic crops producing toxins from Bacillus thuringiensis (Bt) reduce the fitness on non-Bt refuge plants of resistant individuals relative to susceptible individuals. Because costs may vary among host plants, choosing refuge cultivars that increase the dominance or magnitude of costs could help to delay resistance. Specifically, cultivars with high concentrations of toxic phytochemicals could magnify costs. To test this hypothesis, we compared life history traits of three independent sets of pink bollworm, Pectinophora gossypiella (Saunders), populations on two cotton cultivars that differed in antibiosis against this cotton pest. Each set had an unselected susceptible population, a resistant population derived by selection from the susceptible population, and the F1 progeny of the susceptible and resistant populations. Confirming previous findings with pink bollworm feeding on cotton, costs primarily affected survival and were recessive on both cultivars. The magnitude of the survival cost did not differ between cultivars. Although the experimental results did not reveal differences between cultivars in the magnitude or dominance of costs, modeling results suggest that differences between cultivars in pink bollworm survival could affect resistance evolution. Thus, knowledge of the interaction between host plants and fitness costs associated with resistance to Bt crops could be helpful in guiding the choice of refuge cultivars.

A survival cost to mating in a polyandrous butterfly, Colias eurytheme

Adaptations that enhance fitness in one sex may be harmful to members of the opposite sex and lead to antagonistic coevolution between the sexes. In fruit flies, for example, selection for fertilization success has rendered the male ejaculate slightly toxic to females. Here we investigated whether mating imposes a cost upon female fitness in a polyandrous pierid butterfly (Colias eurytheme) by comparing life history traits between once‐mated females and virgins. Mated females laid relatively more eggs early in their adult life, but suffered a reduction in longevity relative to virgins held under identical experimental conditions. The effect of mating on female survivorship was statistically independent of lifetime and early life fecundity. Moreover, lifetime fecundity co‐varied positively with longevity across all females, and across females within each treatment group, hence there was no phenotypic trade‐off between survival and reproduction. These results suggest that the observed longevity difference between virgin and mated females represents a true cost of mating, possibly arising from a toxic side effect of the male ejaculate. However, irrespective of this cost, virgin and mated females laid an equivalent lifetime number of eggs. Female C. eurytheme are also known to use nutrients from the male ejaculate to supplement their reproductive output, hence it is presently unclear how the observed longevity cost may have influenced the evolution of lifetime mating schedules in this polyandrous species.

Screening of Predatory Mites as Potential Control Agents of Pest Mites in Landscape Plant Nurseries of the Pacific Northwest

Abstract To select a biological control agent for suppression of spider mites on landscape plants in western regions of the Pacific Northwest, we compared life history traits of Galendromus occidentalis Nesbitt, Neoseiulus californicus (McGregor) and Neoseiulus fallacis (Garman). We also evaluated abilities of these predatory mites to suppress spider mites in 4 landscape plant species under field conditions. Comparing life history traits from the literature, intrinsic rate of increase was similar between the 2 Neoseiulus species but lower for G. occidentalis. Prey killed per day was greatest for G. occidentalis > N. fallacis > N. californicus. For overwintering abilities, N. fallacis and G. occidentalis are indigenous to the Pacific Northwest and will survive winter assuming overwintering sites are available, but survival of N. californicus is unlikely. Neoseiulus californicus has the widest prey range, G. occidentalis the narrowest, with N. fallacis intermediate. When inoculated into spider mite infested landscape plants, N. fallacis was equally effective at suppressing spider mites as G. occidentalis in either Malus rootstock or Acer shade trees. Further tests with N. fallacis or N. californicus on Spiraea and Rhododendron plants suggested that N. fallacis is equally or more effective at suppressing pest mites, respectively. Compared with the other candidates, N. fallacis was equally effective at controlling pest mites and has a wider prey range than G. occidentalis. Neoseiulus fallacis appears to be the best candidate for biological control of multiple spider mite species on landscape plants in these parts of the Pacific Northwest.

Invasiveness and comparative life-history traits of exotic and indigenous Senecio species in Australia.

A comparative ecological study of closely related invasive and non-invasive species, Senecio madagascariensis and S. lautus (Asteraceae), investigated what traits might confer invasive ability in very similar species. Life-history attributes of the weed S. madagascariensis were compared to five habitat-specific subspecies of S. lautus: S. l. alpinus, S. l. dissectifolius, S. l. lanceolatus and two forms of S. l. maritimus. Field populations of each taxon were monitored to compare their population ecology. Relative rates of phenological development were compared at a single location. Seed germination was studied in a laboratory experiment. Transplant experiments were conducted in a range of S. madagascariensis and S. lautus habitats to compare performance in different environments. In monitored field populations S. madagascariensis produced seedlings and reproductive cohorts more frequently, flowered for longer periods, produced more seeds and had fewer germinable achenes in the soil compared to S. lautus taxa. S. madagascariensis achenes had higher rates of germination than S. lautus in both light and dark conditions. S. madagascariensis was found to have higher rates of survival than S. lautus taxa in a range of habitats and to be faster to flower in both transplant and standard glasshouse environments. Overall S. madagascariensis performed better than S. lautus ecotypes in terms of seedling, growth and fecundity measurements and second best for achenes. Despite relatively good performance in terms of life-history traits there is no evidence that S. madagascariensis is invading S. lautus habitats. We speculate that physiological and morphological adaptations to specialised environments are a better explanation for success of Senecio taxa/ecotypes than generalised life-history trait performance. We suggest that invasiveness is essentially unpredictable, due to habitat/plant specific interactions between invader and area of introduction. In the absence of predictive theory, quarantine authorities should use a combination of methods to assess invasive potential including a database of known weeds, performance comparisons between congeneric natives and exotics in a range of habitats at proposed point of introduction and monitoring of introduced species to determine if they spread.

Dispersal and Life History Traits of Notropis girardi (Cypriniformes: Cyprinidae), Introduced into the Pecos River, New Mexico

-The Arkansas River shiner Notropis girardi was introduced into the Pecos River, New Mexico, in 1978 and was common in collections made in 1986-1987. From collections made since 1978 in the Pecos River drainage, we analyzed patterns of dispersal and abundance, and compared life history traits with a native population of N. girardi from Revuelto Creek, New Mexico. Notropis girardi dispersed downstream, presumably from a single introduction, colonizing much of the mainstream Pecos River (260 km) by 1981. Since 1981, the distribution and abundance of introduced N. girardi has expanded slightly. Age structure, growth and mortality rates of the Pecos River population are similar to those reported in the literature and to a native population of N. girardi in New Mexico. Timing of reproduction was similar for non-native and native populations, and both may exhibit multiple spawning peaks. Notropis girardi reproduction in the Pecos River coincided with large increases in flow. High discharge presumably initiates spawning and promotes downstream dispersal. Similarity of flow regimes of the Pecos River to those formerly found in lotic systems in the native range of N. girardi (e.g., Cimarron River, Kansas and Oklahoma) may account for the relative success of this introduced population.

Life History Traits of the Florida Sand Darter Ammocrypta bifascia, and Comparisons with the Naked Sand Darter Ammocrypta beani

The life history of Ammocrypta bifascia was studied using collections taken from five localities in the Blackwater River drainage, Okaloosa and Santa Rosa counties, Florida, between 1974 and 1977. Ammocrypta bifascia reproduced from April-July or early August. All females were sexually mature by 38 mm SL; and by 43 mm SL, all males were mature. Adult males were significantly larger than adult females. The number of mature ova in 10 females 39.5-52.5 mm SL ranged from 19-85 and was highly correlated with female size. Mean mature ovum diam for nine females were 0.88-1.24 mm (x= 1.08?0.04 mm); individual ova were 0.80-1.33 mm diam. There was no significant correlation between mean female ovum diameter and SL. The maximum life span was ca. 3 years. Individuals matured at about 1 year. Comparisons were made with Ammocrypta beani based on previous work. Ammocrypta bifascia from the Blackwater River drainage of Florida differed from A. beani from the Jourdan River drainage of Mississippi in a number of life history traits. Ammocrypta bifascia matured at a larger size, attained a larger size, reproduced for a shorter period of time, and lived longer. Ammocrypta btfascia females produced fewer but larger ova. INTRODUCTION Published data on the natural history of the Florida sand darter Ammocrypta bifascia are scarce. Williams (1975) provided limited information on the life history of A. bifascia when he described the species. He also discussed the distribution, habitat and common species associates. Bailey et al. (1954) described the habitat and species associates of A. beani ( = A. bifascia) in the Escambia River drainage, Florida. There is no other published information on the natural history of A. bifascia. Herein I present a study of the life history of A. bifascia and compare life history traits of A. bifascia and A. beani based on previous work (Heins and Rooks, 1984). Ammocrypta bifascia is a member of the beani species group in the subgenus Ammocrypta (Williams, 1975; Page, 1981). It occurs in streams of the Gulf Coastal plain of southern Alabama and northwestern Florida from the Perdido River drainage E to the Apalachicola River system (Williams, 1975; Starnes and Starnes, 1979). Ammocrypta bifascia typically is collected in moderate to large streams with shifting sand substrates in moderate current at depths of 2-4 ft; however, it also may be taken in small streams, in streams with swift current, and at depths between 6 inches and 5 feet (Williams, 1975). MATERIALS AND METHODS Collections of Ammocrypta bifascia were taken from five localities in the Blackwater River drainage, Okaloosa and Santa Rosa counties, Florida. The Blackwater River was sampled at two locations. Big Coldwater Creek and the East and West Forks of Big Coldwater Creek each were sampled at one location. The collections were made from 1974-1977 with a 3-m long, 4.8-mm Ace-mesh seine. Specimens were preserved in 10% formalin and stored in 43% isopropyl alcohol. Collections of A. bifascia are deposited in the Florida State Museum at the University of Florida. Climatic and daylength records for the nearest recording stations (Milton Experiment Station and Pensacola, Fla.) were obtained from the National Climatic Center, Asheville, North Carolina, and the Naval Observatory, Washington, D.C., respectively.