Evolution of Protein Molecules

Even among similar-sized organisms a disparity often exists between different species' relative postnatal growth rates. Some authors have interpreted these differences in an adaptive light. That is, some organisms may grow faster than others because it is adaptive to do so (e.g., Lack, 1968). Other investigators have suggested that much of the interspecific variability in growth rates is due to differences in physiological constraints upon growth. That is, all organisms may be growing as fast as possible, but the physiological limits of growth are set at different levels in different organisms (e.g., Ricklefs, 1969, 1973). In the present study, the postnatal growth rates of a variety of reptiles, birds, mammals, and a few fish are compared, in an effort to find evolutionary differences between these vertebrate classes. This analysis suggests that the evolution of endothermy was a key factor in lifting physiological constraints upon growth rates. The maximum observed growth rates of endotherms (except for ...

On the Evolution and Adaptive Significance of Postnatal Growth Rates in the Terrestrial Vertebrates

Toxoplasma gondii is a coccidian parasite which utilizes felids as definitive hosts, and which has an unusually wide intermediate host range The parasite was initially described by Nicolle and Manceaux in 1908 from the rodent, Ctenodactylus gundi Infection with T gondii is one of the most common parasitic infections of man and other warm-blooded animals It has been found worldwide from Alaska to Australia Nearly one-third of humanity has been exposed to this parasite; serologic surveys indicate that T gondii infections are common in wild carnivores, including pigs, bears, felids, fox, raccoons, and skunks Clinical and subclinical toxoplasmosis has been reported from wild cervids, ungulates, marsupials, monkeys, and marine mammals Southern sea otter populations have been severely impacted by Toxoplasma infections

Biology and epidemiology of Toxoplasma gondii in man and animals

The importance of size as a determinant of metabolic rate (MR) was first suggested by Sarrus and Rameaux over 160 years ago. Max Rubner's finding of a proportionality between MR and body surface area in dogs (in 1883) was consistent with Sarrus and Rameaux's formulation and suggested a proportionality between MR and body mass (Mb) raised to the power of 2/3. However, interspecific analyses compiled during the first half of the 20th century concluded that mammalian basal MR (BMR, ml O2 h(-1)) was proportional to Mb3/4, a viewpoint that persisted for seven decades, even leading to its common application to non-mammalian groups. Beginning in 1997, the field was re-invigorated by three new theoretical explanations for 3/4-power BMR scaling. However, the debate over which theory accurately explains 3/4-power scaling may be premature, because some authors maintain that there is insufficient evidence to adopt an exponent of 3/4 over 2/3. If progress toward understanding the non-isometric scaling of BMR is ever to be made, it is first essential to know what the relationship actually is. We re-examine previous investigations of BMR scaling by standardising units and recalculating regression statistics. The proportion of large herbivores in a data set is positively correlated both with the scaling exponent (b, where BMR=aMb b) and the coefficient of variation (CV: the standard deviation of ln-ln residuals) of the relationship. Inclusion of large herbivores therefore both inflates b and increases variation around the calculated trendline. This is related to the long fast duration required to achieve the postabsorptive conditions required for determination of BMR, and because peak post-feeding resting MR (RMRpp) scales with an exponent of 0.75+/-0.03 (95% CI). Large herbivores are therefore less likely to be postabsorptive when MR is measured, and are likely to have a relatively high MR if not postabsorptive. The 3/4 power scaling of RMRpp is part of a wider trend where, with the notable exception of cold-induced maximum MR (b=0.65+/-0.05), b is positively correlated with the elevation of the relationship (higher MR values scale more steeply). Thus exercise-induced maximum MR (b=0.87+/-0.05) scales more steeply than RMRpp, field MR (b=0.73+/-0.04), thermoneutral resting MR (RMRt, b=0.712+/-0.013) and BMR. The implication of this observation is that contamination of BMR data with non-basal measurements is likely to increase the BMR scaling exponent even if the contamination is randomly distributed with respect to Mb. Artificially elevated scaling exponents can therefore be accounted for by the inclusion of measurements that fail to satisfy the requirements for basal metabolism, which are strictly defined (adult, non-reproductive, postabsorptive animals resting in a thermoneutral environment during the inactive circadian phase). Similarly, a positive correlation between Mb and body temperature (Tb) and between Tb and mass-independent BMR contributes to elevation of b. While not strictly a defined condition for the measurement of BMR, the normalisation of BMR measurements to a common Tb (36.2 degrees C) to achieve standard metabolic rate (SMR) further reduces the CV of the relationship. Clearly the value of the exponent depends on the conditions under which the data are selected. The exponent for true BMR is 0.686 (+/-0.014), Tb normalised SMR is 0.675 (+/-0.013) and RMRt is 0.712 (+/-0.013).

https://digital.library.adelaide.edu.au/dspace/bitstream/2440/16422/1/hdl_16422.pdf

Allometric scaling of mammalian metabolism.

Emerging disease and population decline of an island endemic, the Tasmanian devil Sarcophilus harrisii

Aged stages (63) were available for establishment of a timetable of embryonic development of the stripe-faced dunnart. On Day 0 oocytes reaching maturity were found in the ovary. Within +/- 24 h of time 0 (time of minimum morning weight) polymorphonuclear leucocytes appeared and spermatozoa were last detected in the urine of 70% of females. Embryos were collected at intervals during pregnancy by hemihysterectomy and the embryos in the contralateral uterus either were examined at a later stage of pregnancy or allowed to develop to term. Cleavage to the unilaminar blastocyst stage with around 32 cells took 3 days with a cleavage arrest of 24 h at the 4-cell stage. Expansion of the unilaminar blastocyst occurred over the next 3 days. Primitive endoderm cells appeared on Day 6, fully bilaminar blastocysts by the end of Day 7 and trilaminar blastocysts on Day 8. Shell loss and implantation of 13-15-somite stage embryos occurred on Day 8 and organogenesis over the next 2-3 days. The gestation period was 9.5-12.0 days with most births occurring between 10.5 and 11.0 days. Major steps in embryonic development were correlated with stages in the development of the corpora lutea, which were maximal in size, and possibly in secretory activity, when the embryos were at the bilaminar blastocyst stage. Regression commenced when the embryos were at the primitive streak stage. At the time the corpora lutea were maximal the uterine epithelium reached its greatest height and the endometrium was thick and folded. Later in pregnancy villous-like projections of the epithelium formed, and the luminal epithelial cells became rounded. Two cell populations, a tier of 8 smaller cells above the yolk mass and a tier of 8 larger cells around the sides of the yolk mass appeared at the 16-cell stage. From the 16-cell stage to the blastocyst stage, with 150-200 cells, two cell populations distinguished by size, cell cycle time, cytoplasmic appearance and position relative to the yolk mass were present. The two populations were indistinguishable in blastocysts with greater than 200 and less than 2000 cells. They reappeared in blastocysts with greater than 2000 cells, as the darker cells of the embryoblast, and as the paler cells of the trophoblast. The darker cells lay in the yolky hemisphere and the paler cells in the non-yolky hemisphere.

/pdf/a-timetable-of-embryonic-development-and-ovarian-and-uterine-op9l4kapxk.pdf

A timetable of embryonic development, and ovarian and uterine changes during pregnancy, in the stripe-faced dunnart, Sminthopsis macroura (Marsupialia: Dasyuridae).

The exchange of oxygen and carbon dioxide through the skin does not occur in most mammals because they have high metabolic rates and diffusion through the skin is poor. But we have found that in the Julia Creek dunnart (Sminthopsis douglasi), a marsupial mouse with one of the smallest newborns of any mammal, gas exchange through the skin is the predominant form of O2 and CO2 transfer in the first days after birth.

/pdf/breathing-through-skin-in-a-newborn-mammal-674woakrjb.pdf

Breathing through skin in a newborn mammal

Removal of pouch young of Setonix can lead to the resumption of development of quiescent blastocysts. Thirty-six pouch young obtained in this way have been used in this study. As the time in days from resumption of development to parturition is known, accurate ages may be calculated without actual birth or copulation being observed. These 36 animals have been repeatedly measured during their pouch life, and body weight, pes length, and tail length over the full term of pouch occupancy are given as regressions of these measures versus age. Larger-scale regressions are given for the first 80 days of pouch life. A tabulation based on the three regressions and giving average measures at stated ages is also given. During pouch life there is no difference in growth rate between male and female pouch young. Growth proportions of field-reared and compound-reared animals of comparable nutritional status are also similar. It is therefore considered that growth rates are equal, and that the age-estimation procedure established on compound-reared animals is applicable to field animals.

Age estimation by measurement of pouch young of the Quokka (Setonix brachyurus).

The breeding season of S. macroura extends from June to February, and individual males (both wild- caught and laboratory-reared) are capable of breeding over extended periods during the breeding season, and for up to three seasons, in the laboratory. Gross and histological changes in the reproductive organs and endocrine changes in relation to reproductive activity have been investigated. Males do not appear to reach sexual maturity until the season following that in which they were born, although spermatorrhoea may commence in the season of birth. Testis and epididymis weight of these males, which commence spermatorrhoea late in the season, approximates that of sexually mature males early in the season but androgen levels and the weight of the accessory glands are low in all males except during the early months of the season. The age at which spermatorrhoea commences ranges from 141 to 350 days. The minimum scrota1 width at which it commences is 7.9 mm and the minimum body weight, 14.0 g. The onset of spermatorrhoea is not a function of age or season and in S. macroura should be used with caution as an indicator of impending sexual maturity. Maximum corticosteroid- binding capacity (MCBC) generally exceeded corticosteroid concentration and no androgen-related fall in MCBC was evident.

Patricia Ann. Woolley

Papers

A timetable of embryonic development, and ovarian and uterine changes during pregnancy, in the stripe-faced dunnart, Sminthopsis macroura (Marsupialia: Dasyuridae).

Breathing through skin in a newborn mammal

Age estimation by measurement of pouch young of the Quokka (Setonix brachyurus).

Reproduction in Sminthopsis macroura (Marsupialia : Dasyuridae) I. The Female

Carnivore Concerns:. Problems, Issues and Solutions for Conserving Australasia's Marsupial Carnivores