Energy Expenditure and Body Composition in Two Sympatric Lemurs does NOT Support Theories Accounting for Unusual Socio-Ecological Traits and Life History Features

27 03 2010
This image is from Wikimedia Commons and is in the Public Domain

Lemur Catta, also known as the Ring-tailed Lemur

In an article published March 25, in the Online journal PLoS one, researchers present evidence showing no support for the theory that energy conservation behaviors and mechanisms are the result of evolutionary adaptation in response to unusual socio-ecological traits and life history features of those species.

Following is the abstract from the article.  For the complete article, please see the following URL:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0009860.

Abstract

Background

Evolutionary theories that account for the unusual socio-ecological traits and life history features of group-living prosimians, compared with other primates, predict behavioral and physiological mechanisms to conserve energy. Low energy output and possible fattening mechanisms are expected, as either an adaptive response to drastic seasonal fluctuations of food supplies in Madagascar, or persisting traits from previously nocturnal hypometabolic ancestors. Free ranging ring-tailed lemurs (Lemur catta) and brown lemurs (Eulemur sp.) of southern Madagascar have different socio-ecological characteristics which allow a test of these theories: Both gregarious primates have a phytophagous diet but different circadian activity rhythms, degree of arboreality, social systems, and slightly different body size.

Methodology and Results

Daily total energy expenditure and body composition were measured in the field with the doubly labeled water procedure. High body fat content was observed at the end of the rainy season, which supports the notion that individuals need to attain a sufficient physical condition prior to the long dry season. However, ring-tailed lemurs exhibited lower water flux rates and energy expenditure than brown lemurs after controlling for body mass differences. The difference was interpreted to reflect higher efficiency for coping with seasonally low quality foods and water scarcity. Daily energy expenditure of both species was much less than the field metabolic rates predicted by various scaling relationships found across mammals.

Discussion

We argue that low energy output in these species is mainly accounted for by low basal metabolic rate and reflects adaptation to harsh, unpredictable environments. The absence of observed sex differences in body weight, fat content, and daily energy expenditure converge with earlier investigations of physical activity levels in ring-tailed lemurs to suggest the absence of a relationship between energy constraints and the evolution of female dominance over males among lemurs. Nevertheless, additional seasonal data are required to provide a definitive conclusion.

Advertisements




Scientist Shows Post-Mating Pre-Fertilization Barrier to Cross Species Breeding

25 03 2010

Daniel R. Matute of the department of ecology and evolution at the University of Chicago has published a study of two species of Drosophila, that show, for as far as I am aware the first time, the presence of postmating prezygotic isolation.  Specifically, that means a barrier or barriers that act after mating but before fertilization.

The paper appeared on March 23, in the online journal Public Library of Science (PLoS) Biology.  It is important from an evolutionary standpoint as a demonstration of the diversity of ways that reinforcement by gametic isolation can bolster isolation between species or proto-species.

Following is the abstract from the paper.  For the complete paper, please see the following URL:  http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1000341.

Abstract

Reinforcement, a process by which natural selection increases reproductive isolation between populations, has been suggested to be an important force in the formation of new species. However, all existing cases of reinforcement involve an increase in mate discrimination between species. Here, I report the first case of reinforcement of postmating prezygotic isolation (i.e., barriers that act after mating but before fertilization) in animals. On the slopes of the African island of São Tomé, Drosophila yakuba and its endemic sister species D. santomea hybridize within a well-demarcated hybrid zone. I find that D. yakuba females from within this zone, but not from outside it, show an increase in gametic isolation from males of D. santomea, an apparent result of natural selection acting to reduce maladaptive hybridization between species. To determine whether such a barrier could evolve under laboratory conditions, I exposed D. yakuba lines derived from allopatric populations to experimental sympatry with D. santomea, and found that both behavioral and gametic isolation become stronger after only four generations. Reinforcement thus appears to be the best explanation for the heightened gametic isolation seen in sympatry. This appears to be the first example in animals in which natural selection has promoted the evolution of stronger interspecific genetic barriers that act after mating but before fertilization. This suggests that many other genetic barriers between species have been increased by natural selection but have been overlooked because they are difficult to study.





Books: MIT Press Republishes Evolution: The Modern Synthesis

16 03 2010

Evolution: The Modern Synthesis: The Definitive Edition
by Julian S. Huxley, Massimo Pigliucci, and Gerd B. Müller
Paperback – Mar. 31, 2010
MIT Press
784 pages
ISBN-10: 0262513668
ISBN-13: 978-0262513661
SRP: $35.00

This is the original definitive work that gave the name to the Modern Synthesis.  First published in 1942, this re-issue by MIT press makes this ground-breaking work available to modern audiences.  Though now some 68 years old, it is still important (some would say vital) for students of the field to understand the concepts put forward by Huxley and his co-authors, since the Modern Synthesis dominated the field of evolutionary studies for most of the mid- to late-twentieth century.  While evolutionary studies have moved on from the modern synthesis in several key areas, many of the concepts proposed within its covers remain valid today.

The current edition includes the entire 1942 text, Huxley’s introduction to the second edition, published in 1963, and the introduction to the 1974 (third) edition, which was written by nine experts, many of whom were Huxley’s colleagues from various disciplines within evolutionary biology.

The bottom line is that if you study evolution, you should have this work on your bookshelf.