TEMPERATURE, FOOD AVAILABILITY, AND THE DEVELOPMENT OF MARINE INVERTEBRATE LARVAE

Marine invertebrates develop in waters that extend from the poles to t he equator, experiencing the full range of environmental temperature a nd food conditions. How selection has modified their development under the influence of these two factors has been a matter of debate. In th is paper we argue that the primary influence on developmental rate is temperature, while other factors such as food availability are much le ss important. From existing literature we demonstrate that (1) develop mental rates ofboth lecithotrophic and planktotrophic asteroids decrea se in a similar way from the tropics to the poles, as they do also in other groups of invertebrates (echinoids, molluscs, crustaceans), and (2) rates of development at any one temperature cluster around the fun ction describing the effect of temperature, without any relationship t o egg size, suggesting that developmental rates are near the maximum f or a given temperature regardless of other variables such as nutrition . We also investigated the response of development to temperature in f our species of planktotrophic asteroids, one tropical, one temperate, two polar. There was limited temperature compensation among these four species, but little or no apparent ability to compensate for the reta rding effects of reduced temperature within species. Arrhenius analysi s of the data suggests that Q(10) values for the upper region of each species' tolerance range are approximately 2, indicating that enzyme-b ased reactions have evolved to be closely integrated with uncatalyzed, temperature-dependent, physical chemical processes. Values of Q(10) a t lower regions of the tolerance range, on the other hand, range betwe en 9.5 and 14.7, indicative of abrupt temperature-dependent shifts in reaction equilibria, or in the organization of macromolecules and memb ranes. We conclude that temperature itself, rather than egg size, food , or other variables, best explains observed latitudinal differences i n developmental rates in marine invertebrates.