Teresa L. McElhinny

Nocturnal and diurnal rhythms in the unstriped Nile rat, Arvicanthis niloticus

In a laboratory population of unstriped Nile grass rats, Arvicanthis niloticus, individuals with two distinctly different patterns of wheel-running exist. One is diurnal and the other is relatively nocturnal. In the first experiment, the authors found that these patterns are strongly influenced by parentage and by sex. Specifically, offspring of two nocturnal parents were significantly more likely to express a nocturnal pattern of wheel-running than were offspring of diurnal parents, and more females than males were nocturnal. In the second experiment, the authors found that diurnal and nocturnal wheel-runners were indistinguishable with respect to the timing of postpartum mating, which always occurred in the hours before lights-on. Here they also found that both juvenile and adult A. niloticus exhibited diurnal patterns of general activity when housed without a wheel, even if they exhibited nocturnal activity when housed with a wheel. In the third experiment, the authors discovered that adult female A. niloticus with nocturnal patterns of wheel-running were also nocturnal with respect to general activity and core body temperature when a running wheel was available, but they were diurnal when the running wheel was removed. Finally, a field study revealed that all A. niloticus were almost exclusively diurnal in their natural habitat. Together these results suggest that individuals of this species are fundamentally diurnal but that access to a running wheel shifts some individuals to a nocturnal pattern.

Daily rhythms of Fos expression in hypothalamic targets of the suprachiasmatic nucleus in diurnal and nocturnal rodents.

Little is known about the differences in the neural substrates of circadian rhythms that are responsible for the maintenance of differences between diurnal and nocturnal patterns of activity in mammals. In both groups of animals, the suprachiasmatic nucleus (SCN) functions as the principal circadian pacemaker, and surprisingly, several correlates of neuronal activity in the SCN show similar daily patterns in diurnal and nocturnal species. In this study, immunocytochemistry was used to monitor daily fluctuations in the expression of the nuclear phosphoprotein Fos in the SCN and in hypothalamic targets of the SCN axonal outputs in the nocturnal laboratory rat and in the diurnal murid rodent, Arvicanthis niloticus. The daily patterns of Fos expression in the SCN were very similar across the two species. However, clear species differences were seen in regions of the hypothalamus that receive inputs from the SCN including the subparaventricular zone. These results indicate that differences in the circadian system found downstream from the SCN contribute to the emergence of a diurnal or nocturnal profile in mammals.

AGE ESTIMATION AND DISPERSAL IN THE SPOTTED HYENA (CROCUTA CROCUTA)

Abstract We used observations of known-age, free-ranging spotted hyenas (Crocuta crocuta) from a large social group to develop age-estimation models. A model based on tooth-eruption data estimates the ages of animals 10.0–15.5 (±1.1 SD) months old. We used tooth-wear data to estimate the ages of adult males ±4.9 months and ages of females ±22.6 months. Analysis of known and estimated ages shows that males usually disperse from their natal group when 24–60 months of age. Eight of 20 males whose fates were known lived in 3 groups over time, and at least 7 of 41 resident immigrant males appeared to arrive in the study group years after leaving their birthplaces. Thus, males of this species often engage in multiple dispersal events.

Sexual Differentiation of the Zebra Finch Song System Parallels Genetic, Not Gonadal, Sex

Mechanisms regulating sexual differentiation of the zebra finch song system present an intriguing puzzle. Masculine development of brain regions and behavior can be induced in genetic females by posthatching estradiol treatment. That result is consistent with the hypothesis that estradiol, converted within the brain from testicular androgen via the aromatase enzyme, masculinizes neural structure and function. In contrast, treatment during specific stages of development with the aromatase inhibitor Fadrozole has not prevented masculine development, and the presence of testicular tissue in genetic females did not induce masculine organization of neuroanatomy or singing behavior. Fadrozole treatments in those previous studies were limited, however, and most genetic females had both ovarian and testicular tissue. The present experiments were designed to provide increased aromatase inhibition and to reliably produce genetic females with only testicular tissue. Eggs received a single injection at a later age or with higher doses of Fadrozole than had been used previously. Some embryos were exposed to Fadrozole more frequently by either injecting eggs on 2 days of development or dipping them for 10-12 days in Fadrozole. Finally, in some individuals from Fadrozole-treated eggs, the left gonad was removed, leaving each genetic male and female with a single right testis. None of these treatments significantly affected development of the song system compared to appropriate control groups. These results suggest that sexual differentiation of the zebra finch song system is not regulated by embryonic aromatase activity or by gonadal secretions and instead involves events that need not be mediated by steroid hormones.

Biology Undergraduates’ Misconceptions about Genetic Drift

This study explores biology undergraduates’ misconceptions about genetic drift. We use qualitative and quantitative methods to describe students’ definitions, identify common misconceptions, and examine differences before and after instruction on genetic drift. We identify and describe five overarching categories that include 16 distinct misconceptions about genetic drift. The accuracy of students’ conceptions ranges considerably, from responses indicating only superficial, if any, knowledge of any aspect of evolution to responses indicating knowledge of genetic drift but confusion about the nuances of genetic drift. After instruction, a significantly greater number of responses indicate some knowledge of genetic drift (p = 0.005), but 74.6% of responses still contain at least one misconception. We conclude by presenting a framework that organizes how students’ conceptions of genetic drift change with instruction. We also articulate three hypotheses regarding undergraduates’ conceptions of evolution in general and genetic drift in particular. We propose that: 1) students begin with undeveloped conceptions of evolution that do not recognize different mechanisms of change; 2) students develop more complex, but still inaccurate, conceptual frameworks that reflect experience with vocabulary but still lack deep understanding; and 3) some new misconceptions about genetic drift emerge as students comprehend more about evolution.

The Genetic Drift Inventory: A Tool for Measuring What Advanced Undergraduates Have Mastered about Genetic Drift

The Genetic Drift Inventory is a multiple true–false format concept inventory consisting of 22 statements. It tests how well upper-division undergraduate biology students grasp four key concepts, while simultaneously testing for the presence of six misconceptions.

Patterns of Wheel Running Are Related to Fos Expression in Neuropeptide-Y-Containing Neurons in the Intergeniculate Leaflet of Arvicanthis niloticus

Avariety of nonphotic influences on circadian rhythms have been documented in mammals. In hamsters, one such influence, running in a novel wheel, is mediated in part by the pathway extending from neuropeptide-Y (NPY)-containing cells within the intergeniculate leaflet (IGL) of the thalamus to the hypothalamic suprachiasmatic nucleus (SCN). Arvicanthis niloticus is a species in which all individuals are diurnal with respect to general activity and body temperature when they are housed without a running wheel, but access to a running wheel induces a subset of individuals to become nocturnal. In the first study, the authors evaluated the possibility that nocturnal and diurnal patterns of wheel running in Arvicanthis are correlated with differences in IGL function. Adult male Arvicanthis housed in a 12:12 light-dark (LD) cycle were monitored in wheels, classified as nocturnal or diurnal, and then perfused either 4 h after lights-on or 4 h after lights-off. Sections through the intergeniculate leaflet were processed for immunohistochemical labeling of Fos and NPY. The percentage of NPY cells that expressed Fos was significantly influenced by an interaction between time of day and phenotype such that it rose from night to day in diurnal animals, and from day to night in nocturnal animals. In the second experiment, the authors established that running in a wheel actually induces Fos in the IGLof Arvicanthis. Specifically, the proportion of NPY cells expressing Fos was increased by access to wheels in nocturnal animals at night and in diurnal animals during the day. In the third experiment, the authors established that lesions of the IGL eliminate NPY fibers within the SCN, suggesting that these IGL cells project to the SCN in this species as has been established in other rodents. Together, these data demonstrate a clear difference in NPY cell function in nocturnal and diurnal Arvicanthis that appears to be caused, at least in part, by the differences in their wheel-running patterns, and that NPY cells within the IGL project to the SCN in Arvicanthis.

Ontogeny of sexual size dimorphism in the spotted hyena (Crocuta crocuta)

Abstract Body size and growth rate are among the most important traits characterizing an organism, influencing niche occupancy, life-history patterns, mortality rates, and many other fitness components. Sexual size dimorphism is common among animals; in most species females are on average larger than males. In contrast, male mammals are usually larger on average than females of the same species, and the spotted hyena (Crocuta crocuta) may be one of the rare species of mammal in which females are generally larger than males. Nevertheless, some have argued that the evidence is equivocal regarding this reversal. This disagreement may reflect differences in traits measured, methods used, or ontogenetic differences among individuals sampled for these studies. We quantified size at various points during ontogeny in 651 individuals, the largest sample used in size analyses of spotted hyenas to date. We measured 14 morphological traits as well as 4 linear combinations of the traits that provide multivariate estimates of size; these were used to examine growth patterns among males and females measured in a free-living population in Kenya. We demonstrate that female spotted hyenas are larger than males for most, but not all traits, and that females are larger because they grow faster, rather than exhibiting a prolonged period of growth. Early in life males and females appear to grow similarly, but between weaning and reproductive maturity their multivariate ontogenetic trajectories diverge. Traits that mature before divergence of these ontogenetic trajectories are monomorphic, whereas traits that mature later are dimorphic. Furthermore, dimorphism is generally greatest in traits that cease development latest. We propose that later-maturing traits are more dimorphic because of a systemic increase in female growth rates during adolescence that persists through morphological maturity, which varies among traits. We also assess body-size data obtained from captive hyenas to show that adult female hyenas are larger than adult males for some traits even when they are fed identical diets throughout development, allowing us to rule out a strictly environmental explanation for this dimorphism.

The Role of Concept Inventories in Course Assessment

Development of effective instructional materials, particularly those intended to address strongly held alternative conceptions about the natural world, is difficult. Research suggests that the most effective instruction stems from initial consideration of instructional goals and careful alignment of practice with those goals. Understanding whether or not instruction is effective itself requires development of assessment instruments that are written in direct correspondence to pre-articulated goals. Concept inventories (CIs), multiple-choice tests targeting specific content, are becoming increasingly popular mechanisms for assessing student learning, particularly in the USA. CIs have become popular because they target student alternative conceptions authentically and are relatively easy to implement even to very large lecture courses. The wide array of CIs available both in the USA and internationally reflects the importance that faculty place on addressing student conceptions. CIs can be used as both instructional tools and as research instruments; where used for research, scholars must be careful to evaluate the validity and reliability of the CI being used. In this chapter, we provide evidence of the value of CIs for use in both course and programmatic assessment. In addition, we illustrate the importance of community discourse in ensuring that CIs are appropriate for research.