DSpace Angular :: Browsing by Author "Lardies, MA"

Browsing by Author "Lardies, MA"

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Adaptive latitudinal shifts in the thermal physiology of a terrestrial isopod
(2004) Castañeda, LE; Lardies, MA; Bozinovic, F
Temperature is the most important abiotic factor affecting physiology, ecology and evolution in ectotherms. Do organisms broadly distributed along a latitudinal gradient adapt to local differences in temperature? In ectotherms this question has played a central role in evolutionary physiology. By means of an extensive field study and laboratory experiments, we tested the existence of local adaptations in thermal traits along 10degrees of latitude in northern-central Chile. We studied behavioural and thermal traits that have been directly connected with the thermal physiology of ectotherms, along the latitudinal gradient. Using three populations of the common woodlouse (terrestrial isopod), Porcellio laevis, we examined changes in thermal physiology traits (i.e. thermal tolerance, thermal performance) and behavioural traits (i.e. thermoregulation in the field and the laboratory). Performance (i.e. righting response speed) reached a maximum value at intermediate temperatures, and was highest for the northern population. Chill-coma temperature showed an increase towards high latitude, while heat-coma temperature did not vary between populations. On the other hand, optimum temperature was negatively correlated with latitude. Thus, southern woodlice appear to have evolved towards becoming low-temperature specialists, whereas woodlice from warm regions demonstrate low cold tolerance as well as a higher optimum temperature. Our results demonstrate that P. laevis woodlice from different parts of the distribution range show patterns in thermal physiology that covary with the thermal environment (i.e. latitude); thus, P laevis adapts to local environments to increase its performance.
Breeding biology and population structure of the intertidal crab Petrolisthes laevigatus (Anomura: Porcellanidae) in central-southern Chile
(2004) Lardies, MA; Rojas, JM; Wehrtmann, IS
The present study describes the seasonal reproductive cycle and population structure of the porcellanid crab Petrolisthes laevigatus , a typical inhabitant of the rocky intertidal. A total of 960 individuals (including 372 females) was collected in monthly samples from October 1993 to December 1994 in central-southern Chile. Ovigerous females were present between August and December, and were absent between January and July. The breeding season started during late winter (August), and females with embryos close to hatching occurred between October and end of spring (December). Considering the gonadosomatic index and the duration of the incubation period, it is concluded that P. laevigatus has a markedly seasonal breeding period with probably two successive spawnings per female per season. Our results compared with previous studies in temperate intertidal porcellanids suggest a lower structural variability of the population during the sampling period, but a pronounced seasonal variation in both sex ratio and abundance. The influence of environmental habitat conditions (i.e. temperature) is suggested to be responsible for the lower variation in the crab population size structure in ovigerous females, and the almost constant size distribution observed in males.
Effect of oxygen availability in determining clutch size in Acanthina monodon
(2002) Lardies, MA; Fernández, M
Most taxa of aquatic invertebrates exhibit (1) strong variation in number and size of offspring, and (2) an association between adult size and mode of development, and also between mode of development and size of the clutch. These patterns suggest that a similar set of constraints affects both critical life-history traits and physiology of most taxa, Evidence suggests that oxygen is limiting during early development in aggregated egg masses of marine invertebrates. We studied whether oxygen availability during early development could be a determinant of clutch size in the gastropod Acanthina monodon. We estimated intra- and extracapsubar oxygen availability throughout embryo development using optic fibers and incubated capsules at different oxygen partial pressures (hypoxia, normoxia and hyperoxia) throughout development, We also compared the ratio between nurse eggs and embryos in capsules collected in situ as well as in experimental capsules. We found that intracapsular oxygen availability decreased as embryos developed (80% air saturation in early stages to 40% air saturation in late stages), The mean number of embryos increased as oxygen availability increased from hypoxia to hyperoxia, while the total number of eggs remained constant, The mean number of embryos that developed under normoxia was similar to that recorded in field-collected capsules, We suggest that oxygen availability determines clutch size in this species, probably as a result of oxygen competition among siblings, This may also occur in other taxa of marine invertebrates, since oxygen is limiting in egg masses in general.
Effects of environmental variables on burial depth of two infaunal bivalves inhabiting a tidal flat in southern Chile
(2001) Lardies, MA; Clasing, E; Navarro, JM; Stead, RA
The annual pattern of burial depth in natural populations of the infaunal bivalves Tagelus dombeii (Tellinacea) and Venus antiqua (Veneracea) is described in relation to annual food availability in both the water column and the sediment and abiotic factors (temperature and salinity) at Coihuin tidal flat, in southern Chile. A field experiment in which burial depth was measured in situ each month (over 14 months), with the aid of a fixed-length nylon thread attached to the shell. For T. dombeii the results showed a significant increase in burial depth with increasing bivalve size and syphon weight. Tagelus dombeii had a mean burial depth of 17.5 cm, which was three times more than in V. antiqua (5.30 cm). The burial depth dynamics for both species displayed a strong correlation with food availability in the water column. Approximately 60% of the variability in burial depth in T. dombeii and V. antiqua was explained by concentration of chlorophyll-a in the water column. Food concentration on the sediment surface did not effect burial depth, i.e. deposit feeding seems to be of minor significance in either species.
Egg production of Austropandalus grayi (Decapoda, Caridea, Pandalidae) from the Magellan region, South America
(1999) Wehrtmann, IS; Lardies, MA
Austropandalus grayi is one of three pandalid shrimp species reported from Chilean waters. Here we describe fecundity, reproductive output, and chemical composition of the incubated embryos of A. grayi, providing the first account of such information for a pandalid species inhabiting the southern hemisphere. Ovigerous females (n = 96) were collected during October - November 1994 with an Agassiz trawl in waters off Patagonia and Tierra del Fuego, South America. Both egg production (between 50 and 1858 embryos) and early egg volume ((x) over bar = 0.069 mm(3)) of A. grayi were low when compared to values reported from other pandalids. Clutch size increased with maternal size, however, the size of recently spawned eggs was not linked to female size. Although the egg mass volume remained almost stable during the incubation period, females lost on average 51.1% of their initially-laid embryos; however, this loss was more than compensated by an 88.4% increase of the egg volume during embryogenesis. Mean reproductive output was relatively low (0.133) and not related to maternal size. The RO-data of A. grayi and other pandalids seem to indicate an increasing energy allocation for reproduction towards higher latitudes, a trend which would be contrary to the results of studies with other crustaceans. Water was the predominant constituent of the chemical composition of developing embryos and increased from 62.2% to 70.2% during the incubation period. At the same time, organic matter declined and mineral content augmented. Generally, our results are in agreement with previous findings with regard to the chemical composition of developing decapod embryos.
Heritability of progeny size in a terrestrial isopod: transgenerational environmental effects on a life history trait
(2004) Carter, MJ; Lardies, MA; Nespolo, RF; Bozinovic, F
Maternal effects, the environment that mothers provide to their offspring, their provision of nutrients and the environment that offspring of the same clutch share, have come to be recognized as an important influence on offspring fitness. In addition, in invertebrates, maternal effects and common environment may change according to a mother's diet. We tested for the changes in quantitative genetic parameters in a half-sib design where mothers were fed diets varying in nutrient content. Surprisingly, we found that not only maternal and common environmental variance changed with experimental diets but also there were significant changes in narrow-sense heritabilities, with corresponding h(2) values of 0.61 (high protein), 0.08 (high carbohydrate) and 0.001 ( equal carbohydrate: protein). Our results show how an environmentally driven evolutionary process could occur in nature, since the response to selection could change dramatically according to the composition of the diet that females are ingesting.
Interpopulational variation in recovery time from chill coma along a geographic gradient
(2005) Castañeda, LE; Lardies, MA; Bozinovic, F
Extreme temperatures restrict the performance of terrestrial arthropods and variations in low temperatures on it latitudinal scale influence physiological variables. Recovery time from chill coma is a measure of cold tolerance and it is a good index of climatic adaptation. We tested differences in recovery time of the common woodlouse (Porcellio laeris) exposed to different thermal conditions. Individuals were sampled from four dirferent Populations in Chile. spanning a latitudinal range of similar to 10. Significant differences were found in recovery time among experimental temperatures and among populations. but no interaction between these factors. The results of recovery time in P. laeris showed a positive increment with annual mean minimum temperature, indicating that there is geographical variation in recovery time. While body mass presented interopopulational variation. this variation was not associated with thermal variables or latitude. Overall, our results agree with previous Studies in the sense that recovery time from chill coma decreases towards high latitudes, and it is independent of taxa, continent and hemisphere. (c) 2005 Elsevier Ltd. All rights reserved.
Intrapopulational variation in the standard metabolic rate of insects
(2003) Nespolo, RF; Lardies, MA; Bozinovic, F
Studies focusing on physiological variation among individuals, and its possible evolutionary consequences, are scarce. A trait can only be a target of natural selection if it is consistent over time, that is, a trait must be repeatable. In ectotherms it has been suggested that standard metabolic rate (MR) is related to Darwinian fitness, since it reflects energy usage and expenditure. The metabolic rate of the cricket Hophlosphyrum griseus was determined at three ambient temperatures. Repeatability of MR was estimated by product-moment correlation on residuals of body mass, as well as the thermal sensitivity of MR on an individual basis (individual Q(10)). The MR of H. griseus was significantly repeatable (r=0.53) and highly dependent on ambient temperature, and its sensitivity (Q(10)) was dependent on the temperature range. Our estimation of MR repeatability was high in comparison to published studies in vertebrates. Ours is the second report of repeatability (i.e. consistency over time of an individual's performance ranking within a population) of any aspect of energy metabolism in an insect, and also the first study to report significant repeatability of MR. Individual Q(10) values revealed important interindividual variation, which reflects the existence of intrapopulational variability in the thermal sensitivity of MR. In addition, individual Q(10) values were negatively correlated between temperature ranges. This means that crickets having low Q(10) at low temperatures, presented high Q(10) at high temperatures, and vice versa. Our results suggest that MR could be of selective value in insects, showing consistency over time and intrapopulational variability in its thermal dependence. Nevertheless, its heritability remains to be determined.
Latitudinal variation in the reproductive biology of the commensal crab Pinnaxodes chilensis (Decapoda: Pinnotheridae) along the Chilean coast
(2001) Lardies, MA; Castilla, JC
The pinnotherid crab Pinnaxodes chilensis is a common commensal of the edible sea urchin Loxechinus albus along the Chilean coast. Several aspects of the reproductive biology of P. chilensis were examined between April and June 1999, along temperature and salinity gradients, at three sampling sites along the Chilean coast (23degrees45'S-39degrees24'S). Results demonstrated significant differences in egg number, egg volume, dry egg weight, and reproductive output of ovigerous females, between the Studied populations of northern and central-southern Chile. Egg volume, egg dry weight, and reproductive output of females decreased from high to low latitudes, while egg number increased from high to low latitudes, exhibiting a clear trade-off with egg volume. It has been shown that changes in environmental conditions (e.g. temperature, salinity) along a latitudinal gradient, can generate clines in reproductive characteristics in both free-living and parasitic species.
Testing the metabolic cold adaptation hypothesis: an intraspecific latitudinal comparison in the common woodlouse
(2004) Lardies, MA; Bacigalupe, LD; Bozinovic, F
The metabolic cold adaptation (MCA) hypothesis predicts an increase in the metabolic rate of ectotherms from cold environments compared with their more temperate counterparts. This adaptive hypothesis is one of the most controversial in physiological ecology, for which the evidence comes principally from the meta-analysis of data sets of arthropods. Important for the study of metabolic cold adaptation are comparisons at a geographic level, especially on a latitudinal scale, because mean annual temperature decreases towards high latitudes. Furthermore, few studies have conducted intraspecific comparisons of metabolic rates along a latitudinal gradient. We tested the MCA hypothesis in the common woodlouse, Porcellio laevis, using different populations along a distributional range with a wide range of mean ambient temperatures (5degrees, 12degrees, 18degrees and 25degreesC) in Chile. Our results demonstrated that metabolic rate increased towards low latitudes - that is, woodlice from the warmer (i.e. northern) part of the distribution range had markedly higher metabolic rates than those from the cooler (i.e. southern) region, for almost all experimental temperatures. Thus, our results provide direct evidence of intraspecific latitudinal differences in metabolism, rejecting the MCA hypothesis, which is more difficult to resolve with interspecific level comparisons.
The energetics of reproduction and parental care in the terrestrial isopod Porcellio laevis
(2004) Lardies, MA; Cotoras, IS; Bozinovic, F
Parental care is a behavioral strategy that contributes to increased fitness of progeny. Among terrestrial arthropods, many isopods provide extensive parental care. Few studies have quantified the underlying cost of parental care in terms of energy. We used the terrestrial woodlouse Porcellio laevis (Latreille) as a study model to examine how energetic acquisition and expenditure in females is affected during the incubation period and how parental care affects energy balance in this species. We determined the basic reproductive biology (i.e. fecundity, reproductive output, egg volume, egg loss), energy expenditure (i.e. metabolic rate), and energy acquisition (i.e. food consumption, digestibility) of ovigerous females in different stages of embryonic development. Non-ovigerous females were used as the control group. Our results show that P. laevis displays variability in life-history traits compared with populations from other zones around the world. Ovigerous females exhibited a lower ingestion rate and lower digestibility than control females, thus indicating a lower capacity for energy acquisition. Furthermore, energy expenditure was higher in ovigerous females when compared to non-ovigerous females.' In particular, females in early embryonic development stored 5.1-fold less daily energy than females without eggs.

Browsing by Author "Lardies, MA"

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