Crustaceana 86 (1) 16-33

EMBRYONIC DEVELOPMENT AND CARDIAC MORPHOLOGY OF THE GRASS , PUGIO HOLTHUIS, 1949 (, , ): EMBRYONIC STAGING

BY

A. L. ROMNEY1) and C. L. REIBER School of Life Sciences, University of Nevada, Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4004, U.S.A.

ABSTRACT Decapod are known for their variation in developmental patterns and their success- ful adaptation to diverse environmental conditions. The grass shrimp, Palaemonetes pugio Holthuis, 1949, inhabits the brackish waters off the Atlantic and Gulf coasts of North America and is a crit- ically important component of the food chain in these ecosystems. A clear description and under- standing of early embryonic developmental processes is necessary in order for this species to be used for future physiological, ecological, developmental and toxicological investigations. Here, we establish a uniform staging scheme for the embryonic period of development in grass shrimp using an 8-stage sequence. Under constant conditions (20°C, 32 ppt sea water), mean clutch size was 190 (±5) embryos per female and mean time for embryonic development (fertilization to eclosion) was 13 days. Morphological changes and staging were documented using photomicroscopy (still and video). Also described are cardiac morphological changes associated with embryonic development. The morphometrics of both embryonic development and cardiac ontogeny are provided. The mor- phological features described for P. pugio throughout embryonic development and the standardized embryonic staging scheme can be used to compare developmental patterns and timing when inves- tigating questions related to an array of biological disciplines making this species a stronger model system.

RÉSUMÉ Les crustacés décapodes sont connus pour la variation de leur développement et le succès de leur adaptation à diverses conditions environnementales. La crevette, Palaemonetes pugio, peuple les eaux saumâtres des côtes atlantiques d’Amérique du Nord, et est un composé important de la chaîne alimentaire dans ces écosystèmes. Une description claire et la compréhension du début du processus de développement embryonnaire sont nécessaires afin de pouvoir utiliser cette espèce pour de futures investigations physiologiques, écologiques, développementales, et toxicologiques. Nous avons donc établi un plan uniforme de développement comportant une séquence de 8 stades pour la période de développement embryonnaire de cette crevette. Sous conditions constantes (20°C,

1) Corresponding author; e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2013 DOI:10.1163/15685403-00003142 DEVELOPMENT AND CARDIAC MORPHOLOGY OF PALAEMONETES PUGIO 17

32 ppt eau de mer), la taille moyenne d’une portée a été de 190 (±5) embryons par femelle et le temps moyen de développement embryonnaire (de la fertilisation à l’éclosion) a été de 13 jours. Les changements morphologiques et les stades ont été documentés en utilisant la photomicroscopie (photographies et video). Les changements morphologiques cardiaques associés au développement embryonnaire sont aussi décrits. Les données morphométriques du développement embryonnaire et de l’ontogenèse cardiaque sont données. Les données morphologiques décrites chez P.pugio au cours du développement embryonnaire et la standardisation du suivi des stades embryonnaires peuvent êtres utilisées pour comparer les modèles et le temps de développement lorsque seront explorées des questions relatives à tout un ensemble de discipline biologiques, faisant de cette espèce un système modèle solide.

INTRODUCTION The grass shrimp, Palaemonetes pugio Holthuis, 1949, is a decapod native to North American coastal estuaries and collectively an important model or- ganism for physiological, developmental and environmental investigations (Bauer & Abdalla, 2000; Cházaro-Olvera, 2009). Shrimp populations range from Nova Scotia to Veracruz, Mexico (Anderson, 1985) and are an important component to ecosystems (Wood, 1967; Welsh, 1975). Their habitats are typically characterized by extreme environmental variation which leads to physiological stress (Welsh, 1975). The success of this species is related to being uniquely adapted to tolerate wide fluctuations in environmental conditions such as temperature, salinity, and dissolved oxygen (Thorp & Hoss, 1975; Welsh, 1975; Alon & Stancyk, 1982). Developmental patterns in decapods are highly variable both among and within classes yet are also characterized by a number of unified patterns (Anderson, 1973; Gore, 1985). The general pattern of embryonic development seen in this order pro- ceeds from large yolky eggs through naupliar stages and follows with the devel- opment of post-naupliar segments as a forwardly flexed caudal papilla (Anderson, 1973; Gore, 1985). Overlying this basic pattern of development is a number of morphological and physiological adaptations made by individual species allowing exploitation of particular environments (Anderson, 1973; Hartnoll, 1982). Com- paring developmental patterns, one can begin to see the group’s ability to fill an ar- ray of ecological niches. Relevant publications on embryonic development within the family Palaemonidae, along with descriptive staging schemes, include works by Nazari (2000) and Müller et al. (2003, 2007). The embryonic development of crustaceans in a broader sense has been extensively reviewed (Anderson, 1973; Hartnoll, 1982; Gore, 1985). Palaemonid embryonic and larval development is highly sensitive to environment and, as such, well-described developmental stages are needed when investigating physiological and morphological plasticity induced by varying developmental conditions (Rayburn et al., 1996; Ituarte et al., 2005). Embryonic development of P. pugio is initiated by external fertilization of the eggs. The male deposits a spermatophore on the ventral thorax of a mature female,