Changes In Life-history Patterns Research Articles

Interpopulation Plasticity in a Darkling Beetle Life-History along a Whole Oceanic Island Altitudinal Gradient.

Simple SummaryYoung oceanic islands often harbour poor biodiversity because they need time to be colonised. However, some animal species can be abundant, presenting high densities and being widely distributed through different altitudinal habitats of high oceanic islands. This is the case of the darkling beetle Pimelia laevigata costipennis Wollaston, 1864 on El Hierro, the westernmost island of the Canary archipelago. Therefore, this kind of framework is ideal for studying the variation of one insect species in body size, reproductive strategies, and populations in different environments. This study shows how environmental factors related to rainfall and temperature affect the different populations of this flightless beetle. Furthermore, in the more favourable habitats, located at higher altitudes, these beetles were larger in body size, laid clutches with smaller eggs, the reproduction occurred later, and showed the highest population in abundance. Lastly, this is the first study that assesses the changes of an insect along a whole insular altitudinal gradient, demonstrating apparent modifications to each habitat condition.Insects show remarkable phenotypic plasticity in response to changing environmental conditions. The abiotic factors that determine their phenotypes often vary in time and space, and oceanic islands harbour ideal environments for testing predictions on this matter. The ubiquitous beetle Pimelia laevigata costipennis Wollaston, 1864 (Tenebrionidae) is distributed over the entire altitudinal gradient of the island El Hierro (Canary archipelago), from 0 to 1501 m above sea level. Here, we examine how environmental factors (i.e., rainfall and temperature), associated with the altitudinal gradient, affect the body size, reproductive phenology, clutch size and egg volume, and population dynamics of this ectothermic flightless insect. Pimelia l. costipennis populations inhabiting upland localities, typified by lower temperatures, and greater precipitation and vegetation cover, were larger in body size and laid larger clutches with smaller eggs than those in the lowlands. Moreover, reproduction occurred earlier in the year at lower sites and later at higher sites, whereas activity density was highest in the uplands where it increases with temperature. This study first explores the changes in life history patterns along a whole insular altitudinal gradient, and finds interpopulation plasticity. It confirms that environmental factors associated with species spatial distribution act additively as drivers of phenological and phenotypic expression.

Age and growth of grey triggerfish Balistes capriscus from trans-Atlantic populations.

Anthropogenic factors that negatively impact reef fishes can include changes in life-history patterns of fisheries-targeted species. Understanding these impacts on growth and population age structure is essential in the management of exploited populations of fishes. This is the first study to directly compare age and growth for a major fisheries species between east and west populations of a transatlantic reef fish. The main goal of this study was to document age and growth in grey triggerfish Balistes capriscus from coastal waters of Ghana in the Gulf of Guinea (GOG) and compare those with the previous growth studies from that region and with the western Atlantic population. A secondary objective of this study was to evaluate the use of otoliths to age triggerfish and to provide a preliminary comparison with spine-derived age estimates. The results obtained from this study provided an updated understanding of the growth and age structure of the eastern B. capriscus population in GOG. The authors documented that shifts in population attributes occurred for B. capriscus after its major decline in abundance. The differences in physical and biotic characteristics of the East and West Atlantic regions and the differences in collection methods of samples make direct comparisons of growth parameters difficult. Nonetheless, overall differences in maximum sizes and ages were apparent; the western Atlantic population had a larger maximum size and older maximum age. The authors also documented that sagittal otoliths can be used to provide age estimates for triggerfish species, and otoliths as an ageing structure had better between-reader precision compared to dorsal spines.

Genetic Determination of Tolerance to Lethal and Sublethal Copper Concentrations in Field Populations of Daphnia longispina

In order to study the effects of environmental pollution on the genetic diversity of natural populations, two field populations of the cladoceran Daphnia longispina were sampled: one in a reference site (uncontaminated) and the other in a site historically stressed with acid mine drainage (AMD). Five hypotheses were formulated: (1) the stressed population presents a higher tolerance to lethal levels of copper than the reference population, (2) differences in tolerance to lethal levels, observed between the two populations, are due to the loss of sensitive lineages, (3) differences in tolerance to lethal levels of copper between the two populations are due to the appearance of new genotypes, (4) the acquisition of tolerance to lethal levels of copper involved changes in life-history patterns and fitness costs under optimal conditions, and (5) historical contamination by AMD resulted in tolerance differences to sublethal levels between populations, within categories similarly tolerant to lethality, specifically, lineages with similar tolerance to lethal levels from both populations show differences in tolerance to sublethal levels, the stressed population being more tolerant to sublethal levels of contamination than the reference population. Over 125 acclimated cloned lineages, from each population, were exposed to different copper concentrations for 24 hours. At the end of each assay, mortality and feeding inhibition were monitored. Life-cycle traits under optimal conditions were also monitored (time to first brood, number of neonates per brood, inter-brood time, body length, and ingested algae). At lethal levels of copper, significant differences were found in the frequency of sensitive lineages between the two populations. The stressed population did not include the most sensitive lineages, though the most tolerant ones were also present in the reference population. Thus, the hypothesis of presence of new genotypes in the stressed population resulting in an overall increase tolerance of the population at lethal levels was rejected. Changes in life-history patterns were detected, though they were not fully consistent with predictions of life-history theory. Furthermore, these changes in life-history patterns did not involve fitness costs. The fifth hypothesis was rejected since, at sublethal levels of copper, no significant differences were found between the feeding inhibitions of similarly lethal tolerant lineages of the two populations, with only one exception. Therefore, the present study further confirmed the genetic erosion hypothesis and gave further support to the incorporation of genetic diversity measurements into risk assessments.

Haller's Organ in the Tick Family Argasidae (Acari: Parasitiformes: Ixodida)

The structure of Haller's organ in all major groups of soft ticks, family Argasidae, is reexamined, and hypotheses of setal homology are proposed based on a comparative study of developmental patterns. The larvae of most taxa have 7 setae in the anterior pit (1 serrate, 1 conical, 2 fine, 2 porose, 1 grooved) and 4 porose setae in the capsule. The postlarval stages add up to 3 setae to the anterior pit (1 serrate, 1 porose, 1 grooved) and up to 3 porose setae to the capsule. Preliminary hypotheses of polarity, distinguishing ancestral from derived character states, are generated for most characters examined by comparisons with results obtained for the other major family of ticks, Ixodidae, and (where possible) other members of Parasitiformes. Most of the variability in the setal complement of the anterior pit and capsule results from paedomorphosis, and nearly all the observed changes in the setal complement (both modifications of addition patterns and changes in fundamental numbers) are restricted to single species or small species groups. A correlation between changes in Haller's organ structure and changes in life history patterns is suggested but cannot be confirmed based on presently available data.

Comparative Reproductive Strategies of Altricial and Precocial Eutherian Mammals

Mammals produce neonates of varying degrees of development described by the terms altricial and precocial. I rank eutherian mammals by a comprehensive measure of development in which neonates are scored in four areas of independence: thermoregulatory, sensory, locomotory and nutritional. The association between neonatal development and nine life-history traits is examined in 239 species. The distribution of neonatal developmental rankings is associated with adult mass and is related to taxonomic level, with precocial neonates more common among orders, and altricial neonates more common among genera and species. When the effect of adult mass is controlled, precocial mammals produce heavier neonates and heavier litters, possess longer gestation periods, attain adult mass more slowly, and have smaller litter sizes. Mass at weaning, length of the total reproductive interval, and age at first parturition do not differ among developmental categories. Although the continuous nature of development is intuitively appealing, mammalian development patterns do not map onto predictable, continuous changes in life-history patterns. Length of the lactation period is extended in precocial primates but shortened in precocial rodents. Neonate mass varies continuously with stage of neonatal development, while litter size varies dichotomously, and age at first parturition and litter mass differ uniquely in only one developmental category. Thus, neonatal developmental patterns do not appear to result from one continuous axis of selection.