Stephanie F. Anestis

The Apolipoprotein E (APOE) Gene Appears Functionally Monomorphic in Chimpanzees (Pan troglodytes)

Background The human apolipoprotein E (APOE) gene is polymorphic, with three primary alleles (E2, E3, E4) that differ at two key non-synonymous sites. These alleles are functionally different in how they bind to lipoproteins, and this genetic variation is associated with phenotypic variation for several medical traits, including cholesterol levels, cardiovascular health, Alzheimer’s disease risk, and longevity. The relative frequencies of these alleles vary across human populations, and the evolution and maintenance of this diversity is much debated. Previous studies comparing human and chimpanzee APOE sequences found that the chimpanzee sequence is most similar to the human E4 allele, although the resulting chimpanzee protein might function like the protein coded for by the human E3 allele. However, these studies have used sequence data from a single chimpanzee and do not consider whether chimpanzees, like humans, show intra-specific and subspecific variation at this locus. Methodology and Principal Findings To examine potential intraspecific variation, we sequenced the APOE gene of 32 chimpanzees. This sample included 20 captive individuals representing the western subspecies (P. troglodytes verus) and 12 wild individuals representing the eastern subspecies (P. t. schweinfurthii). Variation in our resulting sequences was limited to one non-coding, intronic SNP, which showed fixed differences between the two subspecies. We also compared APOE sequences for all available ape genera and fossil hominins. The bonobo APOE protein is identical to that of the chimpanzee, and the Denisovan APOE exhibits all four human-specific, non-synonymous changes and appears functionally similar to the human E4 allele. Conclusions We found no coding variation within and between chimpanzee populations, suggesting that the maintenance of functionally diverse APOE polymorphisms is a unique feature of human evolution.

Rapid changes in chimpanzee (Pan troglodytes) urinary cortisol excretion

Behavioral endocrinologists are aware that many hormones exhibit a diurnal rhythm, and attempt to correct for this pattern by collecting physiological samples only during specified time windows of varying lengths. In studies utilizing urinary measures of hormone levels, this window often spans 2 h or longer. In this study, we compared chimpanzee urinary cortisol levels in sample pairs collected within 1 h of each other in an attempt to validate the use of a time window for sample collection. Chimpanzees were housed at the University of Louisiana New Iberia Research Center and trained to urinate into a paper cup on command; a total of 41 sample pairs were included in this analysis. We found that mean cortisol levels in the two sets of samples, collected within 1 h or less of each other, were significantly different; the mean cortisol level of the first set of samples was significantly higher than that of the second set. This hormones diurnal pattern of secretion accounts for this significant decrease over a very short time period. We conclude that collection methodologies involving time windows of 1 h or longer need to take into account such rapid changes in levels of excreted hormone. We advocate the use of methodological and statistical corrections to decrease the impact of short-term fluctuations in urinary cortisol.

Specific gravity as an alternative to creatinine for estimating urine concentration in captive and wild chimpanzee (Pan troglodytes) samples.

The measurement of hormones in urine has become a widely used technique in primatology. Because urine concentration varies according to fluid intake, concentration must be measured in each sample collected, and hormone values are always expressed per unit of concentration. Traditionally, creatinine has been used as a concentration index, but some studies in humans have shown that creatinine varies among populations and even within and between individuals within a population, and that it begins to degrade after just one freeze–thaw cycle. In addition, creatinine measurement is relatively time‐consuming and expensive and creates hazardous waste. In this study, we tested the hypothesis that specific gravity, or the ratio of the density of a sample to that of water, is highly correlated with creatinine measurement in urine samples collected from captive chimpanzees at the New Iberia Research Center in Louisiana and wild chimpanzees at the Ngogo study site in the Kibale National Park, Uganda. We found that specific gravity and creatinine were highly correlated in both captive (N=124) and wild (N=13) chimpanzee samples, and that specific gravity measurement was robust to actual and simulated transport conditions and repeated freeze–thaw cycles. We recommend that researchers consider specific gravity measurement as a preferable alternative to creatinine measurement in their studies of primate endocrinology. Am. J. Primatol. 71:130–135, 2009.

Female genito-genital rubbing in a group of captive chimpanzees

Wild and captive female bonobos exhibit a form of noncopulatory sexual behavior—genito-genital (GG) rubbing—in which 2 individuals rub their genital regions together. GG-rubbing in bonobos occurs in several contexts and may serve several functions, including tension reduction and reconciliation. It has not been reported for chimpanzees. In a study of captive, adolescent chimpanzees at the New Iberia Research Center, I observed that females rubbed genital regions at rates equivalent to those of bonobos, though the form of the behavior differed in significant ways from classic bonobo GG-rubbing. I describe the pattern of GG-rubbing in the chimpanzees and provide preliminary tests of 5 hypotheses for why the behavior occurs. All 4 females in the study group participated in GG-rubbing, though the frequency with which they initiated and participated varied. Females that GG-rubbed the most also groomed each other the most, supporting the hypothesis that GG-rubbing reinforces or at least reflects social bonds. The data do not support the hypothesis that females GG-rub to reconcile conflicts, to reduce tension during feeding, to signal social status, or to attract mates.

Primate Personality and Behavioral Endocrinology

Although hormones are best known for their physiological functions, elegant studies in a variety of species have also demonstrated important effects of hormones on behavior (and vice versa: behavior’s effects on hormone levels). Behavioral endocrinology is an exciting field because the relationship between hormones and behavior is complex and in many ways still poorly defined. Initial studies in primates focused primarily on associations between specific behaviors such as aggression or mating and hormones such as testosterone, cortisol, and progesterone. However, as primatologists began to recognize the importance of behavioral style variation and the influence of personality on all aspects of behavior, the physiological correlates of this variable also began gaining attention. In this review, I briefly discuss the mechanisms by which hormones affect behavior before reviewing important research on the role of hormones in maternal style, dominance relationships, and personality. I also discuss the practical and theoretical implications of the relationship between primate personalities and hormone levels. I suggest that this field could benefit from more research in two primary areas: first, the hormonally mediated costs and benefits of certain behavioral styles, and second, personality variation in wild primates and its endocrine correlates.

ORIGINAL ARTICLE: Leptin associations with age, weight, and sex among chimpanzees (Pan troglodytes)

Background  Leptin is a hormone secreted primarily by adipocytes, a lipostatic signal to the hypothalamus, and is often correlated with adiposity. Associations between leptin, age, and development are unknown in human’s closest evolutionary relative, the common chimpanzee (Pan troglodytes).

ORIGINAL ARTICLE: Leptin associations with age, weight, and sex among chimpanzees (Pan troglodytes): Chimpanzee leptin

Background  Leptin is a hormone secreted primarily by adipocytes, a lipostatic signal to the hypothalamus, and is often correlated with adiposity. Associations between leptin, age, and development are unknown in human’s closest evolutionary relative, the common chimpanzee (Pan troglodytes).

A Comprehensive Perspective on Primates

Primates in Perspective offers long overdue, comprehensive coverage of the major extant primate taxa. With 44 chapters and over 700 pages, the editors have clearly compiled this volume with breadth in mind, and in the Preface they state that “we felt it important to create an inclusive volume that reflects the taxonomic, methodological, and theoretical changes that have occurred in primatology since the late 1980s.” This is no small feat, as studies in primatology have multiplied exponentially since that time, and for the most part the editors have achieved this goal. The pitfall of this approach is the loss of coherency that comes with taking on a bit too much, and the inconsistencies that occur when so many authors contribute to one volume. This volume is organized into six sections of drastically different lengths. In Part I: Background (two chapters), Robert Sussman presents a brief overview of primatology from the nineteenth century, and Walter Hartwig presents a brief (ten page) overview of primate evolution suitable for students, both advanced undergraduate and graduate. Sussman’s history, though in fact brief at only four pages, is an engaging summary of key early events in primatology, and includes details from original sources that provide color to stories of early encounters with nonhuman primates. Part II: The Primates (17 chapters) is the longest section, where the major taxonomic groups are introduced. Each ape genus is the subject of a separate chapter, reflecting the fact that the species included in these genera have been very well studied. The chapters are extremely thorough and most provide useful tables with comparisons of the species within the taxonomic group under consideration; e.g., in Chapter 3 Nekaris and Bearder include several excellent tables reviewing the conservation status, completed behavioral studies, ecology, and physical characteristics of the lorisiform primates. If their photographic figures could have been printed in color, they would have been spectacular (and more photographs throughout the volume would have also been a nice addition). Some of the chapters in Part II include not only a review J Mammal Evol (2008) 15:75–77 DOI 10.1007/s10914-007-9060-8