Differences In Life History Characteristics Research Articles

Potential contribution that the copepod Neocalanus tonsus makes to downward carbon flux in the Southern Ocean

We estimate that Neocalanus tonsus makes a contribution to downwards carbon flux of 1.7–9.3 g C m–2 year–1, in subantarctic waters, the Subtropical Front and waters immediately to the north, based on its ontogenetic vertical migration minus the biomass of eggs, the products of which are returned to the surface the following season. This flux is an order of magnitude greater than that estimated (0.27 g C m–2 year–1) for vertical migration of large copepods in the North Atlantic. Over the total 55.6 × 106 km2 where N. tonsus is distributed, 0.17 Gt C year–1 are estimated to be lost annually to the ocean interior. In subantarctic water, this loss represents 1.4% of primary production and is 14% greater than the measured sedimented particulate organic carbon (POC) at 300 m. Similarly, in subtropical water, carbon loss to the ocean interior from N. tonsus seasonal migration is estimated to be 13% lower than measured POC flux. Nevertheless, N. tonsus was never found in time-incremental sediment trap samples. We hypothesize that the apparently proportionally different role of downwards seasonal migration of large copepods relative to sedimented POC in the North Atlantic compared with the subarctic North Pacific and Southern Ocean arises because of a combination of differences in the nutrient status of these oceans, differences in the rate of development of grazer populations in spring, and differences in life history characteristics of large copepods. The flux due to the behaviour of N. tonsus in different parts of its range, put into the context of the estimated global-mean net flux of 1.7–3.7 g C m–2 year–1 taken up by the ocean, may be a regionally significant amount. The summer downward migration of N. tonsus, however, does not entirely explain the observed seasonal variation in regional measurements of pCO2 off New Zealand.

No apparent genetic basis to demographic differences in scarid fishes across continental shelf of the Great Barrier Reef

Two species of parrot fish, Scarus frenatus and Chlorurus sordidus, are known to exhibit demographic and life-history differences across the continental shelf of the northern Great Barrier Reef (GBR). DNA sequences from the mitochondrial (mt) control region were analysed to determine whether there were genetic differences between the populations from the mid- and outer-shelf reefs. Analysis of molecular variance (AMOVA) indicated high levels of gene exchange for both species at a local scale between reefs on mid- and outer continental shelf positions (20 km apart) and at a broader scale along the length of the GBR province (>1000 km apart). There was no evidence to suggest that local differences in scarid life-history characteristics on the northern GBR have a genetic basis. Rather it appears more likely that phenotypically plastic responses to prevailing social and environmental conditions explain differences in the life-history characteristics of both taxa. However, analysis of genetic variation and historical demography revealed striking differences between the two species. S. frenatus haplotypes differed from one another at relatively few nucleotide sites (mean = 3.30), and the pairwise mismatch distribution suggested this species has undergone a population expansion within the limit of the resolution of the marker. C. sordidus haplotypes, however, differed from one another at a number of sites (mean = 7.67). Mismatch distribution analysis suggested that the population size of this species has remained at equilibrium over time. These patterns could also reflect differences in the metapopulation sizes or generation times between taxa. Some of the implications for fisheries management are discussed.

ANADROMOUS SALMONID RECOVERY IN THE UMATILLA RWER BASIN, OREGON: A CASE STUDY1

ABSTRACT: The Umatilla River Basin Fisheries Restoration Plan was initiated in the early 1980s to mitigate salmonid losses caused by hydroelectric development and habitat degradation. The objectives are to enhance the abundance of endemic steelhead and reintroduce extirpated chinook and coho salmon. The project prompted collaborative effort among federal, state, and tribal agencies, and local water users. It has incorporated habitat restoration, flow enhancement, fish passage improvements, and population supplementation through artificial production. Water exchanges have successfully increased minimum flows during spring and fall migration. While flows remain depressed compared to historic conditions, there is potential for improved habitat, passage, and homing. The mean adult‐to‐adult return rate of hatchery‐reared steelhead exceeded replacement and that of the naturally‐spawning population. Although the smolt‐to‐adult survival rates of hatchery‐reared fish fluctuate, salmonid escapement has increased in recent years, permitting steelhead and spring chinook harvest. Enumeration of potential spawners and observed redds reveals an increase in natural production of all supplemented species. Comparison of hatchery‐reared and naturally‐spawning steelhead populations revealed differences in life history characteristics (in age composition and sex ratios) though run timing and genetic stock compositions of the two components of the populations have not differed. Sustained monitoring is needed to determine benefits of integrating habitat restoration and artificial production in restoring salmonid populations.

Life History Characteristics of Three Populations of Edovum puttleri Grissell (Hymenoptera: Eulophidae) at Three Temperatures

Abstract The exotic egg parasitoid Edovum puttleri Grissell has shown promise for biological control of the Colorado potato beetle, Leptinotarsa decemlineata (Say). However, because the activity of currently available populations is decreased at low temperatures, the use of biotypes of E. puttleri adapted to low temperatures may provide more effective control. To determine if there are populations of E. puttleri adapted to low temperatures, the life history characteristics of three populations collected in Honduras were compared at three temperatures (15, 24, and 30°C) over three generations. In general, life history characteristics differed between the first generation and subsequent generations. Among temperatures, parasitoids reared at 24°C were more reproductively active, lived longer, and survived better than those reared at other temperatures. At the lowest temperature, there was a significant difference in the frequency of total egg production, with females from the “River” collection site producing more eggs than females from the other two sites. Coincidentally, the River area is located at the highest elevation and experiences a cooler climate. Comparison of E. puttleri collected in Honduras, Colombia, and Mexico showed differences in life history characteristics. The implications for this study for selection of biotypes of E. puttleri are discussed.

Temperature-related differences in life-history characteristics between diploid and polyploid clones of the Daphnia pulex complex

This study compares life-history characteristics of diploid and polyploid clones of the Daphnia pulex complex at different temperatures to better comprehend their co-existence in the low Canadian arctic. Life-history experiments revealed that polyploid clones had larger eggs and neonates, as well as larger body sizes than diploid clones under 10°C, 17°C, and 24°C. In contrast to high temperature results, polyploid clones matured earlier than diploid clones at 10°C. Our results indicate that polyploid Daphnia may have a headstart over diploid clones at the beginning of the reproductive season when temperature are low. The similarity between cold tolerance in polyploids and organisms with large genomes suggests that it may be large cell size rather than large genomes or hybrid origin that is of selective value in cold environments.

Developmental schedules and persistence of experimental host-parasitoid systems at two different temperatures.

In experimental systems of a bruchid host, Callosobruchus chinensis, and a braconid parasitoid, Heterospilus prosopidis, the effects of changes in developmental schedules were examined in relation to the persistence of the system, or the time to extinction of a component species. We modified the developmental schedules by changing the temperature from 30°C to 32°C. To compare persistence, a long-term system with overlapping generations was set up and the bruchid host resource, azuki beans (Vigna angularis), were renewed every 10 days. The long-term systems showed greater persistence at 30°C than at 32°C. Parasitoid extinction was often observed. We examined differences in life-history characteristics of the component species between the two temperatures by short-term, single-generation experiments. Fecundity and egg hatchability of the host were reduced and the developmental period of the parasitoid was shortened at 32°C. The age at which the host became vulnerable to parasitoid attacks was earlier at 32°C than at 30°C. We constructed a daily based, age-structured model to analyse which life-history change(s) affected the persistence of the long-term systems. The density-dependent population growth of the host was described by a logistic equation and the attack rate of the parasitoid by a type II functional response with mutual interference. The simulation results showed greater persistence at 30°C than at 32°C. Sensitivity analysis showed that there are threshold boundaries in the length of the vulnerable period of the host beyond which system persistence drastically changes. Further, persistence at another temperature, 28°C, was predicted using a model based on short-term data on the host.

Experimental hybridization of alpine and lowland forms of Boeckella dilatata, a calanoid copepod

The freshwater calanoid copepod Boeckella dilatata Sars inhabits lakes and ponds of glacial origin in central and southern South Island, New Zealand. In lowland lakes and ponds, this copepod is small and transparent while in alpine bodies of water, it is larger and bright red. The life history traits of alpine and lowland populations of this copepod also differ. In this paper we present the results of experimental hybridization between individuals from an alpine and a lowland population. Crosses between a transparent, lowland morph of B. dilatata and a red, alpine morph produced viable F1. Intermorph matings showed no sign of reduced clutch size in either alpine or lowland females. Back- and inter-crossing of the F1 showed that this generation was fertile and that subsequent F2 were viable. Clutch sizes of F1 hybrid females backcrossed to lowland males, however, were significantly smaller than those of females in other F1 crosses; in addition, a high variance in clutch size was observed in all F1 crosses, which is also interpreted as reduced fitness. F1 hybrid breakdown was also apparent from the observation that clutch sizes of females in backcrosses with a parental constitution of 25 per cent alpine were significantly smaller than clutch sizes of females in pure crosses. These observations are attributed to heritable differences in life history characteristics between alpine and lowland populations of B. dilatata. We conclude that the red alpine and transparent lowland morphs of this copepod are best regarded as conspecifics in the early stages of speciation and we discuss the results as they relate to current concepts of speciation. F1 and F2 offspring all showed red pigmentation of similar intensity to the original alpine parental generation and we conclude that either pigmentation in B. dilatata is a polygenic character with dominance or is induced by a factor present in the alpine water.

Variation in life history and genetic traits of Hawaiian mosquitofish populations

AbstractMosquitofish (Gambusia affinis) were collected from 17 reservoirs on three islands in Hawaii, USA. Genetic and life history traits for adult females from these populations were used to evaluate hypotheses concerning short‐term evolutionary divergence of populations recently established from a common ancestral source. The effects of founder events and drift on genetic variability and population differentiation were also examined. Significant differences in life history characteristics, allele frequencies, and multi‐locus heterozygosities (H) were found among fish populations collected from different reservoirs and between reservoirs classified as stable or fluctuating on the basis of temporal fluctuation in water level. Females from stable reservoirs exhibited greater standard length (35.1 vs 32.8 mm), lower fecundity (11.9 vs 15.2 embryos), lower reproductive allocation (18.2% vs 22.8%), but larger mean embryo size (1.95 vs 1.67 mg) than females from fluctuating reservoirs. Consistency in means among replicates of each reservoir class and concordance in direction and magnitude of differences reported here and results of sampling conducted from these same locations 10 years previously (Stearns, 1983a) suggest that ecological factors intrinsic to these two environments are important in determing population life history traits.Females from stable reservoirs exhibited lower heterozygosity than females from fluctuating reservoirs (0.134 vs 0.158, respectively). Levels and direction od differences in heterozygosity, the high proportion of polymorphic loci and lack of fixation of alternative alleles argue against a purely stochastic explanation for genetic and life history variation among reservoir populations. Levels of genetic variability and interpopulation differentiation were similar to those observed in mainland populations of this species. A high proportion of the genetic diversity was apportioned between populations and within populations due to differences between juveniles and adults. Significant genotypic differences between adult and juvenile age classes suggest that the genetic divergence of local populations may occur over short periods of time.

Environmental variation, life history attributes, and community structure in stream fishes: Implications for environmental management and assessment

Fishes in midwestern streams of the United States experience strong upstream—downstream gradients in natural environmental variability. Upstream fishes experience greater temporal variability in physical—chemical conditions than downstream fishes, particularly in intermittent streams. Associated with these changes in environmental variability, basic changes occur in life history attributes and temporal variation in community structure of stream fishes. As a whole, upstream species have a shorter life-span, smaller body size, and earlier sexual maturity than downstream species. Descriptive studies also suggest upstream species exhibit more rapid recolonization after severe physical disturbance than downstream species, and fish community structure is temporally more variable in upstream than downstream areas. These longitudinal differences in life history characteristics suggest that upstream fish communities will exhibit more rapid recovery from severe anthropogenic disturbances than downstream fish communities. The greater temporal variability of fish community structure in upstream areas also suggests it will be more difficult in upstream than downstream areas to use fish-based indices to distinguish whether subtle changes in environmental quality are due to natural or anthropogenic disturbances. Long-term monitoring of fishes throughout drainage basins is critically needed to establish more precisely the natural range of variation in community structure. Such monitoring will allow regulatory agencies to distinguish, with greater confidence, the influence of anthropogenic disturbances on stream fishes from the influence of natural environmental variation.

Sex Ratios of Red Maple (Acer Rubrum) Populations in Northern Lower Michigan

Red maple (Acer rubrum) on nine different sites in northern lower Michigan showed generally male—biased sex ratios across a wide variety of habitats and through time. These ratios were not correlated with moisture or nutrient conditions of the sites and for more mesic sites, ratios did not appear to be affected by age of the stands. The more xeric sites showed greater male bias in sex ratios with age of the stand. Within the xeric sites, the sex ratio of regularly flowering trees was more male biased than the ratio of trees at first reproduction. Although data appear to support resource allocation theory predicting more male—biased ratios in older or poorer habitats, the male—biased sex ratios did not result from measurable differences in sex expression of trees originating from sprouts vs. seeds, sex—related differences in size at first reproduction, or sex—related differential mortality, or because of patterns of sex lability. Differences in sex ratio were of minor importance in reproductive success of individuals in the xeric plots given the lack of reproduction from seed. Reproduction from seed was higher in mesic areas, but sex—related differences in life history characteristics were not evident in these areas. The similarity of ratios in a diversity of habitats and through time suggests that the ratios may reflect the underlying genetic patterns of sex expression, rather than subsequent responses to the environment. These data suggest that sex ratios alone are not sufficient to infer proximate mechanisms for biased sex ratios or sex—related differences in resource allocation.

Polyploidy and habitat differentiation in Dactylis glomerata L. from Galicia (Spain).

The microdistribution of diploid and tetraploid plants of Dactylis glomerata L. was examined and related to their immediate environment in several sites in central Galicia, where morphologically indistinguishable individuals of both ploidies grow in sympatry. The two related cytotypes differed in habitat preference. Diploids were mainly confined to the low-density forest-floor habitat in woodlands of mostly ancient origin, whereas tetraploids were widespread in varied habitats but clearly predominant in open areas, particularly in disturbed anthropic sites. The in situ comparison of plant performance showed that where plants of each ploidy were more common they produced more tillers, panicles and seeds. This habitat preference closely reflected differences in life-history characteristics. The tetraploids had an early and short flowering time almost always completed before the aestival drought, whereas the diploids began to flower several weeks later and flowered throughout the drought. Comparisons along artificial gradients of soil water availability and light transmittance indicated that the cytotypes had distinct physiological requirements which probably originated in metabolic and more general genetic differentiation and could be directly attributable to ploidy. Habitat differentiation increases the species' colonizing ability. It also amplifies divergence in reproductive strategy between diploids and tetraploids, which reduces ineffective crossing between cytotypes and thereby permits them to coexist in sympatry. The effect of hybridization at the polyploid level on the differentiation between cytotypes was assessed from the recent introduction of a foreign tetraploid entity into the study area. Hybridization between the two distinct tetraploids was found to increase habitat differentiation between the diploids and the tetraploids, but the major part of this differentiation is probably attributable to ploidy itself.

Environmental heterogeneity and life history variability in the freshwater clams, Pisidium variabile (Prime) and Pisidium compressum (Prime) (Bivalvia: Pisidiidae)

The pisidiid clams, Pisidium variabile (Prime) and Pisidium compressum (Prime), from permanent ponds in southwestern Ohio are iteroparous, bivoltine, and have approximate longevities of 1 year. Intrapopulation differences in life history characteristics are discussed in relation to environmental heterogeneity. For the P. variabile population, only age at first reproduction (110 and 226 days for the spring and fall generations, respectively) is different for both annual generations. This is due to differences in environmental variables (temperature, dissolved oxygen levels, food availability) which set physiological limits on growth, reproduction, and maintenance functions. The spring and fall generations of P. compressum show differences in several life history characteristics: age at first reproductive (122 and 270 days, respectively), net reproductive rate (8.7 and 3.7, respectively), r (0.005 and 0.003, respectively), and the number of broods per year (2 and 1, respectively). The results of this study tend to question the validity of using current theories (e.g, r- and K-selection, bet-hedging) which attempt to predict the set of demographic characteristics that should be found in populations under varying environmental circumstances.

Growth Rate in Island and Mainland Anoline Lizards

Growth data for Anolis lizards were fitted to the logistic growth equation and the calculated rate constant was used for interpopulation comparisons of growth rates. The major result was that most of the relatively small-sized anoles studied belong to one of two exclusive groups: Insular species with low growth rates and mainland species with high growth rates. As a result of their lower growth rates, the age at sexual maturity is greater for island (5-9 months) than for mainland species (2-4 months). This dichotomy in growth rate and age at sexual maturity supports the hypothesis that island anoles may be generally food limited and mainland anoles not so limited and suggests other differences in life history characteristics for these two groups of anoles.