Facultative paternal investment in the polyphenic beetle Onthophagus taurus: the role of male morphology and social context

Members of a population often differ significantly in theirparental investment. Such variation is generally believed tohave important consequences for mating system evolution andhas been suggested to play an important role in the evolutionof some secondary sexual traits and displays. Recent studiessuggest that individuals are able to adjust the intensity and kindof parental investment they provide according to the breedingconditions they encounter. As a consequence, between-individualvariation in parental investment may depend more on externalconditions than previously thought for these taxa. This mayhave important implications for current perspectives on therole of differential parental investment in the evolution andmaintenance of certain mating systems and sexual selection regimes.Here I quantify patterns of variation in paternal investmentas a function of social conditions in a species of beetle thatis dimorphic for male horn morphology. I demonstrate that undercertain conditions (namely, the absence of other males), paternalassistance covaries with male morphology, with horned males investingsubstantially more time in assisting females than hornless males.I also show that the magnitude of differences in paternal investmentbetween male morphs varies in response to external conditions.In the presence of other males, paternal assistance was negligiblefor both male morphs, who instead invested substantially andequally in mate-securing behaviors. I use my findings to discussthe significance of variation in paternal assistance for onthophaginemating systems and evaluate ideas proposed to explain the evolutionof alternative morphologies in the genus Onthophagus.     

Reproductive indicators in natural populations of Douglas-fir in Mexico

The reproductive capacity in nine Mexican Douglas-fir populations was determined by analyzing seed production traits from 144 trees collected in 2001. Significant variation was found for all traits among populations; they contributed between 21% and 43% of total phenotypic variation found in these traits, indicating broad differences in reproductive capacity for that particular year. Seed efficiency (filled seed/seed potential) varied from 14% to 42% among populations; all populations from Central Mexico had a seed efficiency below 25%. The proportion of developed that were empty seeds varied from 0.40 to 0.81 among populations, whereas seed size varied also from 0.88 to 1.21 g per 100 seeds among them. Average ratio of filled seed weight to cone weight (reproductive efficiency) was 29.6 mg g⁻¹, but it varied three-fold between populations with extreme values. Populations with larger cones had greater seed potential and heavier seed but not necessarily higher reproductive or seed efficiency. Most reproductive indicators were significantly correlated with latitude, with lower values in the marginal populations from Central Mexico, in the southern extreme of the species range. Given these results, the need for conservation of Douglas-fir populations in Central Mexico is discussed.     

Organizational effects of estrogen on male-type vulnerability to early weaning

We previously reported that early-weaned (postnatal day 14) male ICR mice, compared to normally weaned animals, exhibited a persistent increase in anxiety-related behavior in the elevated plus maze test. In this study, we examined whether steroid hormone manipulations on postnatal day 0 and at the ages of 2 or 3 weeks affected male-type vulnerability to early weaning. Neither castration nor ovariectomy at the age of 3 weeks affected male-type vulnerability. However, in males, castration at the age of 2 weeks attenuated the increased anxiety levels induced by early weaning, and the implantation of testosterone or estradiol, but not of dihydrotestosterone, restored the effects of early weaning. In contrast, in females, neonatal treatment with testosterone propionate together with testosterone at the age of 2 weeks, which reversed sexual behavior to the male type, did not affect anxiety levels in response to early weaning. When pregnant females were repeatedly treated with testosterone propionate on embryonic days 14, 17, and 19, in addition to testosterone treatment at the age of 2 weeks, the anxiety levels in female were increased by early weaning. Furthermore, the prenatal treatment of estradiol benzoate, but not dihydrotestosterone, induced enhanced anxiety levels by early weaning in females. These results suggest that neural systems are masculinized by estrogen from the embryonic phase to the early postnatal period and are responsible for the high levels of anxiety elicited by early weaning.     

Populations and assemblages of parasites in hake, Merluccius gayi, from the southeastern Pacific Ocean: stock implications

To assess fish stocks, the populations and community assemblages of metazoan parasites were compared in 1172 Chilean hake Merluccius gayi landed at two major ports, and caught during 1991–1992 in three major fishing areas off central Chile. At least two ecological stocks are suggested, based on consistent differences in parasitism between body length classes for Grillotia dollfusi, Hysterothylacium sp., Clestobothrium crassiceps and Aporocotyle wilhelmi . More use should be made of the information on whole parasite assemblages including, for example, patterns of co-occurrence of parasite species. Univariate analyses on selected taxa in samples from different areas may show no differences because of the same prevalence or abundance for each parasite taxon, but opposite numerical arrangements of co-occurring taxa in community assemblages would remain undetected.     

Developing ecosystem objectives for the Great Lakes: policy,progress and public participation

Under the Great Lakes Water Quality Agreement of 1978 between the United States and Canada, as amended in 1987, an ecosystem objective with associated indicators for Lake Superior was adopted, and a commitment was made to develop ecosystem objectives and indicators for each of the other Great Lakes. Building upon a history of activities within the International Joint Commission related to the development of ecosystem indicators for Lake Superior and for mesotrophic waters, a binational Ecosystem Objectives Work Group (EOWG) has been established by the U.S. and Canada and charged with developing ecosystem objectives for the Great Lakes, beginning with Lake Ontario. These objectives are primarily biological in nature, in contrast to chemical objectives. The approach of the EOWG is to identify in sequence: (1) broad ecosystem goals, (2) a suite of objectives whose attainment would ensure achievement of the goals, and (3) one or more measurable indicators of progress toward meeting each objective. Societal values are reflected in the goals and objectives following consultation with competing users of ecosystem resources. Identification of appropriate indicators requires the assistance of technical experts. The experience of the EOWG in developing ecosystem objectives for Lake Ontario illustrates the application of this process.