Demographic Characteristics of Female Mottled Sculpin, Cottus Bairdi, in the Coweeta Creek Drainage, North Carolina

We quantified: (1) growth rate, (2) length-mass relationships, (3) size- and age-specific fecundity, (4) egg size-frequencies, and (5) size- and age-specific egg diameter relationships for reproductively active female C. bairdi from one of the southern-most extant populations of this species (Coweeta Creek drainage, North Carolina). Gravid females were collected during February and March in 1993–1995, and 1998. Cottus bairdi reached an age of 7+ and 79mm standard length. The youngest and smallest gravid female collected was a 41mm 1+ individual. Mature 1+ females were not uncommon and we collected 21 during our study. All females older than age 2 were mature. Mean fecundity for C. bairdi at Coweeta was 71 eggs (range 9–166 eggs). We found significant positive relationships between fecundity and female length, weight and age. Female length and weight also significantly affected mean egg diameter, although the relationship was not linear. Neither female size or age significantly affected mean maximum egg diameters. Female C. bairdi from the Coweeta Creek drainage possess a unique suite of reproductive characteristics that may represent adaptations to the local selective regime or ecophenotypic variation.     

The cost of reproduction in the glaucous-winged gull

Summary Experimental enlargement of brood size in the glaucous-winged gull (Larus glaucescens) resulted in increased adult foraging time, decreased adult body weight at the end of the breeding season, and decreased over-winter adult survival. The decreased survival of breeding adults was associated with reduced body condition at the end of breeding (resulting from physiological costs of reproduction). Decreased survival was not due to an increased risk of injury or predation during the breeding season. Brood size did not directly affect the fecundity of surviving birds in the subsequent year. However, brood size may have an indirect effect on subsequent fecundity because the probability of mate loss increased among birds with large broods and the reproductive performance of birds with new mates was reduced. Based on estimates of life-time fitness calculated from fecundity and survivorship, birds with two- or three-chick broods (the normal brood size) have higher fitness than birds with one- or four-chick broods. However, the decreased fitness of birds with four-chick broods was slight, and probably not a sufficient explanation for the absence of natural four-chick broods in the glaucouswinged gull.     

Résistance et viabilité des gamètes d'Omble de fontaine,Salvelinus fontinalis, à différents pH

Résumé Afin d'étudier les effets de l'acidité lors de la fécondation chez l'Omble de fontaine, la motilité des spermatozoïdes, l'absorption d'eau par les oeufs et la survie de ceux-ci ont été déterminées à différents pH. Les poissons fournissant les gamètes utilisés pour ces tests provenaient de lacs acides ou non acides.Pour les valeurs de pH inférieures à 5,0, la proportion de spermatozoïdes motiles diminue rapidement et devient nulle à pH 3,0. A pH 4,0, cette proportion est plus élevée dans une solution d'acide sulfurique, qui est totalement dissocié, que dans une solution d'acide acétique, faiblement dissocié. Dans cette dernière, la quantité d'ions H⁺ neutralises par le sperme est environ cinq fois plus élevée que dans la solution d'acide sulfurique.La pression osmotique du milieu de fécondation ainsi que l'origine des géniteurs, provenant de lacs acides ou non, affectent également la résistance des spermatozoïdes.L'absorption d'eau par les oeufs est diminuée à pH 5,2 ou 4,5 selon l'origine des géniteurs. La survie des oeufs est peu affectée pour des pH de 4,5 et plus, mais est réduite à pH 4,0.L'ensemble des résultats permet d'avancer qu'un pH de 4,5 représente la limite inférieure compatible avec une bonne fécondation chez l'Omble de fontaine; cette limite semble cependant susceptible d'être modifiée par la présence d'acides faibles dans le milieu et par l'origine des géniteurs.

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Variations in acidity were shown to have pronounced effects on the gametes of Salvelinus fontinalis collected from populations living in acid or circum-neutral lakes.Spermatozoa motility was reduced at pH less than 5.0 and ceased at pH 3.0. Within this range, motility was greater in the presence of strongly dissociated acid (H₂SO₄) than in a weakly dissociated one (CH₃COOH). In the latter solution, at pH 4, sperm neutralized 5 times as many H⁺ as in the former. Differences in spermatozoa motility were observed depending upon the origin of the gametes and the osmotic pressure of the medium.Egg survival was reduced at pH 4. Water absorption by eggs decreased below pH 5.2 or 4.5 for eggs collected from circumneutral or acid lakes, respectively.These results suggest that pH 4.5 represents the lower limit for successful fertilization of eggs of brook trout, the precise point depending upon the types of acid present and the origin of the parental stock.

     

Egg shape and size allometry in geckos (Squamata: Gekkota), lizards with contrasting eggshell structure: why lay spherical eggs?

Hard, highly calcified eggshells evolved several independent times during the history of amniotes. Because of phylogenetic conservatism of this trait, lineages in which closely related taxa differ in eggshell structure are rare. Four gekkotan families (Carphodactylidae, Diplodactylidae, Eublepharidae and Pygopodidae) have eggs with soft shells, while their close relatives (Gekkonidae) lay eggs with hard shells. Geckos thus offer a rare opportunity to compare the impact of the emergence of a hard eggshell on the economy of egg architecture. Because a sphere has the smallest surface area of all three‐dimensional solids of a given volume, spherical eggs in geckos with hard eggshells reduce calcium investment and should therefore be advantageous. Here, we document that hard‐shelled gekkonid eggs are indeed more spherical than those of the other gecko lineages. However, within gekkonids, small species lay more elongated eggs than larger species. We speculate that miniature gekkonid females, which lay larger eggs relative to body size compared with large gekkonids, produce elongate eggs in order to pass the egg through a limited pelvic opening.     

Biology of the mysid Mesopodopsis slabberi (van Beneden, 1861) (Crustacea, Mysidacea) in a coastal lagoon of the Ebro delta (NW Mediterranean)

Aspects of the population and reproductive biologyof the mysid Mesopodopsis slabberi were studiedin the western Mediterranean (Encanyissada coastallagoon, Ebre delta, Spain). Misids were sampling atmonthly intervals from August 1993 to June 1995. InDecember 1994 and February 1995 any individuals werefound. The relationship between carapace length (Lc)and total length (Lt) was isometric:logLt = 1.0612logLc + 0.9411 (n = 178,r = 0.9411). Thesize of mature males and females was at a maximum inthe winter, and a minimum in the summer. The longevityof individuals changed throughout the year; those withthe longest life expectancy were members of theoverwintering generation. Brooding females wererecorded throughout the year, except in December 1993and April 1994; they were most numerous in spring andautumn. The number of embryos or larvae (N) carried byfemales was related to the size of the females (range:1–22, mean value: 4.8): logN = 1.8705logLc–0.0985(n = 361, r = 0.4097, P < 0.01). Thesize of the eggs(maximum diameter, Le) was related to the size of thefemales (range: 0.35–0.6 mm in total length):logLe = 0.3404logLc–0.4820 (n = 277, r = 0.5420, P < 0.01).     

Lifetime reproductive effort in humans

Lifetime reproductive effort (LRE) measures the total amount of metabolized energy diverted to reproduction during the lifespan. LRE captures key components of the life history and is particularly useful for describing and comparing the life histories of different organisms. Given a simple energetic production constraint, LRE is predicted to be similar in value for very different life histories. However, humans have some unique ecological characteristics that may alter LRE, such as the long post-reproductive lifespan, lengthy juvenile period and the cooperative nature of human foraging and reproduction. We calculate LRE for natural fertility human populations, compare the findings to other mammals and discuss the implications for human life-history evolution. We find that human life-history traits combine to yield the theoretically predicted value (approx. 1.4). Thus, even with the subsidized energy budget and uniqueness of the adult lifespan, human reproductive strategies converge on the same optimal value of LRE. This suggests that the fundamental demographic variables contained in LRE trade-off against one another in a predictable and highly constrained manner.     

Multiple-year optimization of conservation effort and monitoring effort for a fluctuating population

We consider optimal conservation strategies for an endangered population. We assume that juvenile survival is affected by unpredictable environmental fluctuation and can be improved by costly conservation effort. The initial population size is not accurately known at the time that the conservation effort level is chosen, but the uncertainty of its estimate can be reduced by a costly monitoring effort. In a previous paper, we analysed the optimal management strategy that minimizes a weighted sum of extinction probability and economic costs when only a single year is considered. Here we examine the case in which the conservation period lasts for several years by dynamic programming with incompletely observed process states. We study the optimal levels of the conservation and the monitoring efforts, and their dependence on the length of the conservation period and other parameters. The main conclusions are: (1) The optimal conservation effort in the first year depends on the accuracy of the information on the population size in the first year, but is almost independent of the accuracy of the information in later years. (2) When the risk of population extinction is small, the optimal conservation effort increases with the uncertainty of the population size. In contrast when the population is endangered, the optimal conservation effort decreases with the uncertainty of the population size. (3) The optimal conservation and monitoring efforts both increase with the length of the conservation period, provided that the population is relatively safe. However, if the population is endangered, both types of effort become smaller when the conservation period increases.     

The corn snake yolk sac becomes a solid tissue filled with blood vessels and yolk-rich endodermal cells

The amniote egg was a key innovation in vertebrate evolution because it supports an independent existence in terrestrial environments. The egg is provisioned with yolk, and development depends on the yolk sac for the mobilization of nutrients. We have examined the yolk sac of the corn snake Pantherophis guttatus by the dissection of living eggs. In contrast to the familiar fluid-filled sac of birds, the corn snake yolk sac invades the yolk mass to become a solid tissue. There is extensive proliferation of yolk-filled endodermal cells, which associate with a meshwork of blood vessels. These novel attributes of the yolk sac of corn snakes compared with birds suggest new pathways for the evolution of the amniote egg.