Spatial aspects of movements, mating patterns, and nest distributions influence gene flow among population subunits of Blanding’s turtles (Emydoidea blandingii)

The core habitats of semi-aquatic organisms are centered on wetlands, but also include terrestrial habitats. Patterns of movements among core area components can influence rates of genetic and demographic exchange among populations. A combination of 33 years of data on the life history and spatial biology of Blanding’s turtles (Emydoidea blandingii) on the E. S. George Reserve (ESGR) and 8 years of genetic data (N = 244 adults and 611 offspring) were used to document resident wetlands, identify mating pairs, and estimate cohort levels of coancestry and degree of spatial genetic structuring. For ESGR resident females, 34 % of clutches were sired by non-resident males, whereas 56 % of clutches of non-resident females that nested on the ESGR were sired by ESGR resident males. The mean number of mates for males and females was 1.6 (SD = 0.67) and 2.02 (SD = 1.05), respectively, and the annual occurrence of multiple paternity averaged 47.6 % (min–max = 15.4–55.6 %, N = 8). Repeat paternity was common (69.6 %), regardless of residence of parents. The probability of adults mating with individuals from different residence wetlands and tendencies for hatchlings to disperse to wetlands other than their mother’s residence contributed to demographic and genetic connectivity among residence wetlands. Similar allele frequencies among individuals from different residence wetlands (F_st = 0.002, P > 0.05) were consistent with the frequency and geographic extent of adult and juvenile movements. Data on mating patterns, individual movements, and core-habitat use helped identify mechanisms that influence genetic structuring within a population comprised of multiple sub-units.     

An organ culture system to model early degenerative changes of the intervertebral disc

Introduction  

Back pain, a significant source of morbidity in our society, is related to the degenerative changes of the intervertebral disc. At present, the treatment of disc disease consists of therapies that are aimed at symptomatic relief. This shortcoming stems in large part from our lack of understanding of the biochemical and molecular events that drive the disease process. The goal of this study is to develop a model of early disc degeneration using an organ culture. This approach is based on our previous studies that indicate that organ culture closely models molecular events that occur in vivo in an ex vivo setting.     

Study of the mitotic and meiotic chromosomes of sotol (<i>Dasylirion cedrosanum</i> Trel.)

The genus Dasylirion is a group of plants typically present in the Chihuahuan Desert, perennial, with a dioecious sexual behavior and commonly called sotoles. This genus has been little studied from the biological point of view, and the bases of its reproductive response remain unknown. In this work we studied the chromosome number and meiotic response of Dasylirion cedrosanum in the county of Saltillo, Coahuila, located at the North East of Mexico. For the preparation of mitotic chromosomes, we used a technique based on enzymatic treatment with pectolyase and cellulase, as well as staining with acetocarmin dye. For the study of meiosis, male flower buds were collected, fixed and stained for analysis with the same dye. As a result, the gametic (n = x = 19) and somatic chromosome (2n = 38) numbers of D. cedrosanum are reported for the first time, being consistent with previous findings in other Dasylirion species, which points to a constant ploidy level across the genus. Variation was observed in the morphology and size of the somatic chromosomes, with types ranging from submetacentric to subtelocentric, and sizes oscillating in a range of 4.43 µm, with an average total length of 112.38 µm for the diploid chromosome complement. This shows that the chromosome complement of D. cedrosanom would belong to a 3B classification of Stebins, with a medium variation between chromosome lengths and low chromosome asymmetry. This variation indicates the feasibility of constructing a chromosome ideotype for this species. The meiotic chromosome pairing showed a chromosome behavior consistent with a disomic inheritance characteristic of a diploid species, with prevalence of ring and chain bivalents, typically without pairing abnormalities. Bivalent configurations in all cases were symmetrical.The normal and symmetrical meiotic pairing indicates a balanced production of gametes, and suggests the absence of heteromorphic sex determination.     

The utility of nuclear introns for investigating hybridization and genetic introgression: a case study involving Brachyramphus murrelets

Interspecific hybridization can have importantconsequences for conservation, but can bedifficult to detect using morphologicalmarkers. To test the utility of nuclear intronsfor investigating hybridization and geneticintrogression, we analyzed variation in fivenuclear introns and the mitochondrialcytochrome b gene in two species ofseabirds that are declining and may behybridizing: marbled murrelets(Brachyramphus marmoratus) and Kittlitz'smurrelets (B. brevirostris). No alleleswere shared between samples of the two species,and intron alleles formed reciprocallymonophyletic groups in gene trees. Our resultssuggest that few murrelets in Alaska areF ₁, F ₂or back-cross hybrids,and that gene pools of these species have beenindependent for 1.8 to 5.7 million years. Weconclude that introns are a potentially richsource of markers for analyzing hybridizationand introgression in endangered or decliningspecies.     

Intersexual differences in energy expenditure of Anolis carolinensis lizards during breeding and postbreeding seasons

Although the amount of energy that males and females invest in reproduction is an integral component of theories explaining the evolution of particular mating strategies, few studies have actually determined the amount of energy that each sex allocates to reproduction. We compared how energy is expended by male and female Anolis carolinensis lizards during both the breeding and postbreeding seasons. We used laboratory respirometry to determine resting metabolic rates (RMRs) of inactive, freshly captured lizards and the doubly labeled water technique to determine field metabolic rates (FMRs) of free-ranging lizards. Both RMRs and FMRs were influenced by body mass but not by sex. Season did not influence FMRs; however, RMRs of both sexes increased approximately 40% from the breeding to the postbreeding season. The seasonal increase in RMRs was attributed to a postreproductive increase in feeding rate and specific dynamic action. We used RMRs, FMRs, and thermal profiles of lizards to calculate energy budgets for breeding and postbreeding seasons. Energy budgets partitioned daily field energy (DFE; calculated from FMRs) into daily activity energy (DAE) and daily resting energy (DRE; calculated from RMRs). Energy expended for reproduction was estimated as DAE during the breeding season plus egg production (for females). Despite males having 40% greater body mass, females expended 46% more energy for reproduction than did males (906 and 619 J/d, respectively). Total metabolizable energy (TME=DFE+egg production for females) expended during the breeding season was similar for males and females (1,280 and 1,365 J/d, respectively). Although TME of females decreased 44% from the breeding to the postbreeding season (1,365 vs. 766 J/d), TME of males was similar during both seasons (1,280 vs. 1,245 J/d). There were both seasonal and sexual differences in DRE and DAE. Compared with most lizards from semiarid/desert habitats, A. carolinensis in a temperate habitat expends more total energy during the breeding season, allocates more energy to eggs, and appears to have more total energy available for reproduction.     

Microclimates and energetics of free-living box turtles, Terrapene carolina, in South Carolina

We measured microclimate, field metabolic rates (FMRs), water flux, and activity patterns of telemetered box turtles (Terrapene carolina) in South Carolina from September 1987 to October 1988. Turtles were inactive for most of the winter and were active only sporadically during the rest of the year. Using the doubly labeled water method, we found that water flux averaged 8.8, 18.9, and 26.4 mL kg(-1) d(-1) in winter, spring, and summer/fall, respectively. FMR for the same periods averaged 0.028, 0.065, and 0.124 mL CO(2) g(-1) h(-1). Differences in FMR among seasons were significant but not between sexes. Using operative temperatures, we predicted standard and maximum metabolic rates of turtles. In winter, FMR was elevated above standard metabolic rates and close to maximum metabolic rates, whereas in spring and summer/fall, FMR fell midway between standard and maximum metabolic rates. We used a model to predict metabolic rates, geographical distribution, and potential reproductive output of box turtles across latitudes in eastern North America. Low FMR and low annual reproductive output may allow box turtles to survive and flourish in unpredictable resource environments by minimizing costs and risks, thereby maintaining greater lifetime reproductive success.     

The influence of circadian rhythms on pre- and post-prandial metabolism in the snake Lamprophis fuliginosus

Measuring standard metabolic rate (SMR) and specific dynamic action (SDA) has yielded insight into patterns of energy expenditure in snakes, but less emphasis has been placed on identifying metabolic variation and associated energy cost of circadian rhythms. To estimate SMR, SDA, and identify metabolic variation associated with circadian cycles in nocturnally active African house snakes (Lamprophis fuliginosus), we measured oxygen consumption rates (VO2) at frequent intervals before and during digestion of meals equaling 10%, 20% and 30% of their body mass. Circadian rhythms in metabolism were perceptible in the VO2 data during fasting and after the initial stages of digestion. We estimated SMR of L. fuliginosus (mean mass=16.7+/-0.3 g) to be 0.68+/-0.02 (+/-SEM) mL O2/h at 25 degrees C. Twenty-four hours after eating, VO2 peaked at 3.2-5.3 times SMR. During digestion of meals equaling 10-30% of their body mass, the volume of oxygen consumed ranged from 109 to 119 mL O2 for SMR, whereas extra oxygen consumed for digestion and assimilation ranged from 68 to 256 mL O2 (equivalent to 14.5-17.0% of ingested energy). The oxygen consumed due to the rise in metabolism during the active phase of the daily cycle ranged from 55 to 66 mL O2 during digestion. Peak VO2, digestive scope, and SDA increased with increasing meal size. Comparisons of our estimates to estimates derived from methods used in previous investigations resulted in wide variance of metabolic variables (up to 39%), likely due to the influence of circadian rhythms and activity on the selection of baseline metabolism. We suggest frequent VO2 measurements over multiple days, coupled with mathematical methods that reduce the influence of undesired sources of VO2 variation (e.g., activity, circadian cycles) are needed to reliably assess SMR and SDA in animals exhibiting strong circadian cycles.     

Close genetic similarity between two sympatric species of tephritid fruit fly reproductively isolated by mating time

Abstract.— Two sibling species of tephritid fruit fly, Bactrocera tryoni and B. neohumeralis , occur sympatrically throughout the range of B. neohumeralis in Australia. Isolation between the two species appears to be maintained by a difference in mating time: B. tryoni mates at dusk, whereas B. neohumeralis mates during the middle of the day. A morphological difference in humeral callus color also distinguishes the two species. Despite clear phenotypic evidence that B. tryoni and B. neohumeralis are distinct species, genetic differentiation as measured by four markers–nuclear DNA sequences from the white gene and the ribosomal internal transcribed spacer (ITS2), and mitochondrial DNA sequences from the cytochrome b (cytb) and cytochrome oxidase subunit II (COII) genes–is very small. Minor fixed differences occur in the ITS2 sequence, however, in all other cases the two species exhibit a high level of shared polymorphic variation. The close genetic similarity suggests either that speciation has occurred very rapidly and recently in the absence of any mitochondrial DNA sorting or that the sharing of polymorphisms is due to hybridization or introgression. A third species within the tryoni complex, B. aquilonis , is geographically isolated. Bactrocera aquilonis is also genetically very similar, but in this case there is clear differentiation for the mitochondrial loci. The three species form a group of considerable interest for investigation of speciation mechanisms.