Wittmann 1984a
Wittmann 1984a
WITTMANN, K. J., 1984a: Ecophysiology of Marsupial Development and Reproduction in Mysidacea (Crustacea). Oceanography and marine Biology. An annual Review, 22: 393-428.
All species of the order Mysidacea lay their eggs in a brood pouch thus allowing direct study of the development of young from oviposition to attainment of the juvenile stage. In recent years increasing interest has been focused on the development of young and its ecological and physiological demands and implications. This has been accompanied by increasing efforts and success in experimentation and the culture of the animals. Besides their traditional rôle in fisheries biology and in food chain studies, mysidaceans have recently become important as test organisms in work on the ecological and physiological effects of pollutants (see review by Nimmo Hamaker, 1982). The present review is mainly concerned with the ecophysiological importance of incubation in mysidaceans. This importance may be direct or indirect; it may reflect the effects of certain factors on incubation or the implications of incubation for other ecological or biological processes. In fact, it is shown in the following that the duration of incubation bears more and stronger implications on reproductive and population ecology than was previously thought. The incubation period appears to be a key factor for the understanding of variations in the length and timing of the breeding season, age at maturity, frequency of broods, numbers of young per brood, egg size, and adult body size. This review may initiate search for similar relationships in other groups of brood-protecting marine poikilotherms. These relationships are of fundamental importance to the whole complex of reproductive and population ecology. In this way the present study may give valuable background information for almost any kind of study dealing with biology, population ecology or ecophysiology in mysidaceans.
Recently Mauchline (1980) has reviewed the biology of mysidaceans and I have drawn freely on some of the data presented in his tables. He dealt with the broad field of the biology but did not go into so much detail as far as incubation is concerned. Nevertheless, some overlap in our studies appears to be inevitable. I have not included some important topics such as sex ratio, differential mortality of sexes, and growth, age, and numbers of moults at sexual maturity. For these fields of interest one should consult Mauchline's (1980) study.
GENERAL CONCLUSIONS FOR THE UNDERSTANDING OF BREEDING BIOLOGY IN MYSIDACEANS
There are two basically different groups, semelparous and iteroparous mysidaceans. Differences are apparent not only in generation times and timing of breeding but also in the allometric relationships between parents and young. The latter differences appear to be due to the number of broods per se as in the case of semelparity there is neither the necessity nor the possibility of synchronizing development and production of subsequent broods. There is no doubt that semelparity is of advantage in high latitudes due to the low temperatures in combination with the short duration of the favourable season. It is, however, known also from the giant bathypelagic species G. ingens which probably lives in a relatively stable environment. Childress Price (1978) discuss the possible advantage of semelparity for this species and state. . . because of the greater stability of its habitat it can . . . concentrate all its reproductive effort on a single event. This may be much more energy efficient, since the reproductive individual can use a larger fraction of its energy in reproduction . . .. This remains speculative as long as there are no weight or energy measurements which compare broods and breeding females. Volumetric studies of Mauchline (1973) indicate that the meso- and bathypelagic species including G. ingens invest on the average the same fraction of body volume in reproduction as do epipelagic species.
In iteroparous mysidaceans the breeding biology is split into three highly different levels which involve differences (1) between latitudes, (2) between seasons (provided that there is a strong seasonal climate), and (3) between individuals.
Natality and relative fecundity, as defined above, both appear to be constant between latitudes but undergo strong seasonal variations. Natality increases with increasing individual size but, as far as is known, relative fecundity does not seem to vary with variations in size. Absolute fecundity expressed as numbers of young per brood increases with increasing latitudes in relation to temperature. At the favourable season absolute fecundity is high, but at or shortly before the onset of the unfavourable season, fecundity is low and largely independent of seasonal variations in body size and temperature. Brood sizes increase linearly, or possibly less than linearly, with individual body weight. In contrast to this, brood size increases with about the square root of weight between latitudes.
Egg weights increase with increasing latitudes in relation to temperature in about the same way as do brood sizes. Egg sizes may not vary between seasons in certain species or a species may produce larger winter eggs and smaller summer eggs. There seems to be no direct relation to temperature as the production of the larger eggs may start in early autumn at water temperatures as high as 20-25°C, while on the other hand, the production of small summer eggs may start in late spring at about the same temperatures (pers. obs. on Leptomysis lingvura in the Gulf of Naples). There appears to be no correlation between egg sizes and individual parental body sizes.
As a consequence of the foregoing, the production of yolk per egg per incubatory day does not vary between latitudes and also not, as far as is known, between individuals. There may, however, be strong variations between seasons. Weight at attainment of maturity and brood weights, both increase between latitudes almost twice as steeply with increasing temperature than do brood sizes and egg weights. In temperate climates, summer animals are frequently smaller than winter ones, but similar frequently maximum sizes may be reached in spring. Similar relations may exist for brood weights. These increase about linearly with individual body weights. The same relation was found to exist between latitudes or species. Among seasons this relation is heavily `disturbed' by variations in brood weight due to minima or maxima in breeding intensity.
The key factor for the understanding of these relationships seems to be the temperature effect on incubation periods. It is strong between latitudes, but much weaker between seasons. There are no visible differences in the temperature response between individuals of L. lingvura (Wittmann, 1981b). There is a small effect of egg size on incubation periods which is about the same between latitudes and among individuals. Wittmann's (1981b) results indicate that this is also most likely between seasons. Each of three levels of breeding performance are supposed to be indicative of different adaptive significance. Between latitudes reproduction appears to be adaptive in order to compensate for the strong effects of temperature on incubation periods. Among seasons the seasonal variations of food supply and, as an outcome of these, variations of population levels seem to be of major significance. For individuals it may be of major importance that a given increase in body weight becomes transformed into a corresponding increase of individual reproductive fitness, expressed as production of young per incubatory day. This indirectly favours the capability of adapting population levels to ambient food levels.
physiology; reproduction; growth; development
Acanthomysis longicornis; Acanthomysis sculpta; Antarctomysis maxima; Boreomysis arctica; Diamysis bahirensis; Gastrosaccus lobatus; Gastrosaccus psammodytes; Gastrosaccus vulgaris; Gnathophausia ingens; Hemimysis speluncola; Leptomysis buergii; Leptomysis gracilis; Leptomysis lingvura; Lophogaster; Mesopodopsis orientalis; Metamysidopsis elongata; Metamysidopsis insularis; Mysidacea; Mysidium columbiae; Mysidopsis bahia; Mysidopsis bigelowi; Mysis litoralis; Mysis mixta; Mysis oculata; Mysis relicta; Mysis stenolepis; Neomysis americana; Neomysis integer; Neomysis intermedia; Neomysis japonica; Neomysis mercedis; Paramysis intermedia; Paramysis pontica; Paramysis ullskyi; Praunus flexuosus; Praunus inermis; Praunus neglectus; Schistomysis spiritus; Siriella armata; Siriella clausii; Siriella jaltensis