Copepod post-embryonic durations: pattern, conformity, and predictability. The realities of isochronal and equiproportional development, and trends in the opepodid-naupliar duration ratio

Abstract

A collation of post-embryonic durations for freshwater and marine calanoid, cyclopoid and harpacticoid copepods is provided, and examined for patterns and conformities which may be of predictive value. Most of the analysis concerns calanoids. Only the genus Acartia exhibits evidence of equal stage duration (isochronality). Accordingly, isochronal development must be rejected as a general pattern in copepods -with various implications to the study of their production. Conversely, relative stage durations are surprisingly comparable in a wide range of copepods across a broad range of temperatures and food levels. A loose consistency is evident among copepod species generally, (interspec@ equiproportionality), but within given genera, a striking regularity, here termed intergeneric equiproportionality (IGE) is evident.Patterns of IGE are consistent with selectively adaptive life-history traits, and IGE thus offers predictive prospects which are of both quantitative and qualitative (heuristic) value. Empirical support which exists for IGE among marine calanoids suggests that in contrast to isochronality and interspecific equiproportionality, IGE is indeed a real, and ultimately quantifiable feature of copepod development.Within calanoids, the ratio of total copepodid to total naupliar duration (DclDn) appears independent of temperature, shows little relationship to adult body mass, but is inversely related to food supply, markedly so in freshwater forms. In this context, changes in the ratio are attributable largely to influences of food supply upon copepodid development times : naupliar durations appear relatively independent of food concentrations during development. Considerably higher DclDn ratios in freshwater than in marine calanoids conceivably arise from selective influences of different nutritional conditions and size-selective predation pressures in freshwater and marine environments. In the generally high predation environment of freshwaters, acceleration of naupliar development potentially reduces the vulnerability of these smaller stages to size-selective tactile predation, while larger copepodid instars are able to reduce the opposing size-selective influences of visual planktivores by virtue of their escape responses to suction attack. Within the spectrum of copepod life histories and development schedules, ecologically consistent trends of this nature await formal recognition. The present recognition of IGE is a modest initiative in this quest.Both naupliar and copepodid durations are inverse monotonic functions of temperature. Several mathematical expressions which account for this temperature-duration response are provided. The response envelope is much tighter for naupliar than copepodid durations. Predictability of temperatureduration responses accordingly declines ontogenetically from egg to naupliar to copepodid stages.

Body size regulation in copepod crustaceans

“…This limitation is not purely conceptual; logistically, it has been difficult if not impossible to measure individual size nondestructively, particularly of larval copepod (naupliar) stages. This difficulty has severely limited our understanding of the range of factors affecting individual growth and body size (Thompson 1982;Hart 1990;van den Bosch and Gabriel 1994 ), including factors that might constrain body size.…”

Influence of algal diet on growth and ingestion of Calanus helgolandicus nauplii

“…Ontogenetic differences in the physiological response to temperature in copepods have also been noted (Pedersen & Tande 1992). The effect of food quantity on growth processes has often been unclear (Hart 1990, Hopcroft & Roff 1998, but some studies have clearly established an effect of food limitation on wild nauplii (Lopez 1991, Melle 1998, and this has been further substantiated by laboratory studies (Green et al 1991, Lopez 1996.Food quality is another factor which has to be considered when examining variability in naupliar growth (Mullin & Brooks 1970, Paffenhöfer 1971, 1976, Fernández 1979a,b, Diel & Klein Breteler 1986, Verity & Smayda 1989. The major algal characteristics of importance are biochemical content, morphology, and digestibility of the algae (e.g.…”

Exuvium analysis: A nondestructive method of analyzing copepod growth and development

“…In particular, naupliar developmental patterns are poorly known. Hart's (1990) summary of existing data on postembryonic instar durations shows little support for isochronal development, except for species of the marine Calanoid Acartia (e.g. Landry 1975;Miller et al 1977).…”

“…Despite their importance, these processes are difficult to quantify for small, mobile, aquatic organisms like copepods, and particularly for the earliest, naupliar stages (e.g. Thompson 1982;Hart 1990). Techniques developed to measure growth and development often yield mean stage-specific values that are of questionable value for a population, given that age and size vary considerably among individuals, even under uniform, optimal rearing conditions (e.g.…”

“…Landry 1975;Miller et al 1977). There is more support for equiproportional development, although Hart (1990) claims that only intergeneric equiproportionality has any sound biological basis or predictive ability. Some of the confusion over appropriate growth rules may result from the fact that not all individuals in a population (or family) exhibit the same patterns of growth and development, as we found for individual B. triarticulata and B. hamata.…”