Molly Gould

In many species females choose a mate from among several available males; in other species, the social system provides no apparent opportunity for making a decision among alternative suitors, and decision-making capacity is assumed to be minimal. The origins, bases, and logic of female mate choices are contentious questions with important cognitive implications. Female short-finned mollies, Poecilia sphenops, have never been observed to choose mates in the wild, where instead a male-contest social system prevails. Nevertheless they readily choose between models of males in the laboratory. Some of their decisions anticipate features found in males in more recently evolved species where the social system permits female choice. The willingness of females to choose traits in a species without such traits or evident need or opportunity for female choice in the wild is remarkable. These observations suggest that choice behavior can be latent in a species, and may direct or bias the development of behavioral preferences.

Sexual selection is a possible mechanism of speciation. This could be true even in systems where female mate choice has not been clearly observed, because pre-existing biases may be expressed if female decision-making results in male trait evolution. In some mollies, males have enlarged dorsal fins and courtship display is the prevailing mating process. In others, male dominance is thought to play a greater role. We tested females of a species in the latter group, Poecilia mexicana, for consistent preference related to dorsal fin morphology. We found that females were biased toward larger dorsal fins. This latent preference could be an important driver in trait evolution.

Twenty-five children with acquired immunodeficiency syndrome (AIDS) underwent cranial magnetic resonance imaging and proton magnetic resonance spectroscopy. Patients were divided into 2 groups based on clinical parameters: encephalopathy and nonencephalopathy. N-acetyl aspartate/creatine ratios were compared between the 2 groups and to control data. Spectra were obtained for 2 volumes of interest: the basal ganglia region and the white matter. The mean basal ganglia region ratio for the AIDS encephalopathy patients (n = 8) was 1.12 and the ratio for the AIDS nonencephalopathy patients (n = 17) was 1.48. The ratio for the 9 controls was 1.57. The encephalopathy group had a significantly lower ratio than both the control (P < .001) and the AIDS nonencephalopathy group (P < .002). The mean white matter ratio for the encephalopathy group (n = 8) was 1.47 and for the AIDS nonencephalopathy group (n = 13) was 1.82 with a control (n = 6) ratio of 1.82. The encephalopathy patients had a lower white matter ratio than the nonencephalopathy (P < .05) patients but the ratio was not different than controls (P < .11). It is concluded that N-acetyl aspartate/creatine ratios are reduced in childhood AIDS encephalopathy and proton magnetic resonance spectroscopy may be helpful in defining brain human immunodeficiency virus-1 infection. However, further longitudinal studies are necessary to determine the sensitivity and specificity of this technique.