The escape of veligers from the egg capsules of Nassarius obsoletus and Nassarius trivittatus (gastropoda, prosobranchia)

Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology [and the Woods Hole Oceanographic Institution] June 1975Many species of prosobranch gastropod deposit their eggs in tough capsules affixed to hard substrates. Generally, there is a small opening near the top of such capsules, occluded by a firm plug (operculum) which must be removed before the veligers can escape. Although the removal of the operculum is generally attributed to embryonic secretion of enzymes, there is little experimental support for this sugsestion. In the limited experiments which have been reported, all dealing with species that emerge as juvenile snails, no attempt was made to determine the properties of the hatching substance, or the timing of its production. My research has dealt with the escape of veligers from the egg capsules of two related species, Nassarius obsoletus and N. trivittatus. Their egg capsules are quite similar in size, number of eggs contained, general morphology, and the thickness of the material plugging the opening at the top. Both hatch as swimming veligers, after about one week of encapsulated. development. By adding fresh plug material to small volumes of sea-water containing veligers obtained prior to, or at known times after their normal hatching, I have demonstrated conclusively the essentially chemical nature of operculum removal for these two species. In addition, the hatching substance was found to be produced in a short pulse, to be functionally short-lived, and to be species-specific in its action for the two species considered. There is no evidence that the secretion of the hatching substance is stimulated by short pulses of light or increased temperature; the capsules of N. obsoletus contain many more embryos than are needed to successfully remove the plug, so that complete synchrony of hatching substance production by all individuals within a capsule is probably not necessary. Lastly, the observed rates at which N. obsoletus veligers leave their egg capsules were compared with those predicted from an equation assuming random movement of individuals. A close agreement was found, the capsules losing 98% of their residents within 45 to 55 minutes of the first escape. Thus, the location of the exit by an individual is probably by chance.This work was supported by a graduate fellowship from the Woods Hole Oceanographic Institution

Understanding the Effects of Low Salinity on Fertilization Success and Early Development in the Sand Dollar Echinarachnius parma

Free-spawning marine invertebrates that live near shore or in estuaries may experience reduced fertilization success during low-salinity events. Although several studies have documented reproductive failure at reduced salinity in estuarine animals, few have looked at whether developmental failure is due to a failure of fertilization or to a failure of fertilized eggs to cleave. In this study, we examined the effects of salinities ranging from 18 to 32 psu on fertilization success and early development in the sand dollar Echinarachnius parma. In addition to decoupling the effects of low salinity on fertilization from its effects on early cleavage, we also assessed whether eggs or sperm were the weak link in accounting for reproductive failure. We found that both fertilization and cleavage failed at salinities below about 22 psu but that development could be partially rescued by returning zygotes to full-strength seawater. We also found that sperm remained active and capable of fertilizing eggs even after being exposed to low salinities for 30 min.. Taken together, these results suggest that reproductive failure at low salinities in E. parma is due more to an inability of the fertilized eggs to cleave than to an inability of sperm to fertilize eggs

K-theoretic Schubert calculus and applications

A central result in algebraic combinatorics is the Littlewood-Richardson rule that governs products in the cohomology of Grassmannians. A major theme of the modern Schubert calculus is to extend this rule and its associated combinatorics to richer cohomology theories. This thesis focuses on K-theoretic Schubert calculus. We prove the first Littlewood-Richardson rule in torus-equivariant K-theory. We thereby deduce the conjectural rule of H. Thomas and A. Yong, as well as a mild correction to the conjectural rule of A. Knutson and R. Vakil. Our rule manifests the positivity established geometrically by D. Anderson, S. Griffeth and E. Miller, and moreover in a stronger 'squarefree' form that resolves an issue raised by A. Knutson. Our work is based on the combinatorics of genomic tableaux, which we introduce, and a generalization of M.-P. Schuetzenberger's jeu de taquin. We further apply genomic tableaux to obtain new rules in non-equivariant K-theory for Grassmannians and maximal orthogonal Grassmannians, as well as to make various conjectures relating to Lagrangian Grassmannians. This is joint work with Alexander Yong. Our theory of genomic tableaux is a semistandard analogue of the increasing tableau theory initiated by H. Thomas and A. Yong. These increasing tableaux carry a natural lift of M.-P. Schuetzenberger's promotion operator. We study the orbit structure of this action, generalizing a result of D. White by establishing an instance of the cyclic sieving phenomenon of V. Reiner, D. Stanton and D. White. In joint work with J. Bloom and D. Saracino, we prove a homomesy conjecture of J. Propp and T. Roby for promotion on standard tableaux, which partially generalizes to increasing tableaux. In joint work with K. Dilks and J. Striker, we relate the action of K-promotion on increasing tableaux to the rowmotion operator on plane partitions, yielding progress on a conjecture of P. Cameron and D. Fon-der-Flaass. Building on this relation between increasing tableaux and plane partitions, we apply the K-theoretic jeu de taquin of H. Thomas and A. Yong to give, in joint work with Z. Hamaker, R. Patrias and N. Williams, the first bijective proof of a 1983 theorem of R. Proctor, namely that that plane partitions of height k in a rectangle are equinumerous with plane partitions of height k in a trapezoid

Crepipatella dilatata (Lamarck, 1822) (Calyptraeidae): An example of reproductive variability among gastropods

Reproductive characteristics of a species are often defined from a small number of individuals collected from a single location at one particular time. However, this study reveals that the South American gastropod Crepipatella dilatata (Lamarck, 1822) shows an unusually high level of intraspecific variability in some key reproductive characteristics: the number of egg capsules brooded per female, the size of the egg capsules, the number of eggs per capsule and the sizes and size distributions of the uncleaved eggs. Larger females were more fecund than smaller ones, not because they produced more egg capsules, but because they produced capsules of significantly larger size. Such variability was evident not only when considering different populations, but also within a single population sampled in different years, as well as among specimens collected during a single sampling event. Thus our data emphasize the importance of obtaining information from numerous specimens per locality as well as from specimens from different localities and in different years when describing the reproductive characteristics of any particular taxon.Facultad de Ciencias Naturales y Muse

Crepipatella dilatata (Lamarck, 1822) (Calyptraeidae): an example of reproductive variability among gastropods

Fil: Zelaya, Diego Gabriel. División Zoología Invertebrados. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Pechenik, Jan A.. Biology Department. Tufts University. Medford; USAFil: Gallardo, Carlos S.. Instituto de Zoología. Universidad Austral de Chile. Valdivia; Chil

Extinction Rates for Fluctuation-Induced Metastabilities : A Real-Space WKB Approach

The extinction of a single species due to demographic stochasticity is analyzed. The discrete nature of the individual agents and the Poissonian noise related to the birth-death processes result in local extinction of a metastable population, as the system hits the absorbing state. The Fokker-Planck formulation of that problem fails to capture the statistics of large deviations from the metastable state, while approximations appropriate close to the absorbing state become, in general, invalid as the population becomes large. To connect these two regimes, a master equation based on a real space WKB method is presented, and is shown to yield an excellent approximation for the decay rate and the extreme events statistics all the way down to the absorbing state. The details of the underlying microscopic process, smeared out in a mean field treatment, are shown to be crucial for an exact determination of the extinction exponent. This general scheme is shown to reproduce the known results in the field, to yield new corollaries and to fit quite precisely the numerical solutions. Moreover it allows for systematic improvement via a series expansion where the small parameter is the inverse of the number of individuals in the metastable state

Temporal Variation in Cyprid Quality and Juvenile Growth Capacity for an Intertidal Barnacle.

Abstract. Implicit in past studies of recruitment is the assumption that all new recruits possess the same capacity for juvenile growth, and that observed variation in juvenile growth and survival is due entirely to spatial and temporal variation in food availability, magnitude of physical stresses, and intensity of competition and predation. We set out to determine if daily larval cohorts of the barnacle Semibalanus balanoides differ in mean physiological quality and, therefore, in their potential for recruiting to adult populations. To assess larval physiological quality, we measured the organic content of nonfeeding cyprid larvae attaching on five dates (10-15 d intervals) during the 1995 recruitment season. Juvenile physiological quality was determined by monitoring the growth, under controlled laboratory conditions, of individuals attaching on seven dates (3-15 d intervals) during the same season. Both cyprid organic content and juvenile growth capacity differed significantly among daily cohorts. We suggest that variation in cyprid organic content may explain previous observations of temporal variation in cyprid metamorphic success and early juvenile mortality and further suggest that variation in juvenile growth capacity contributes to differences in recruitment success of daily cohorts