The Implications of Temperature-Mediated Plasticity in Larval Instar Number for Development within a Marine Invertebrate, the Shrimp Palaemonetes varians

Abstract

Variations in larval instar number are common among arthropods. Here, we assess the implications of temperature-mediated variations in larval instar number for larval development time, larval growth rates, and juvenile dry weight within the palaemonid shrimp, Palaemonetes varians. In contrast with previous literature, which focuses on terrestrial arthropods, particularly model and pest species often of laboratory lines, we use wild shrimp, which differ in their life history from previous models. Newly-hatched P. varians larvae were first reared at 5, 10, 17, 25, and 30°C to assess their thermal scope for development. Larvae developed at 17, 25, and 30°C. At higher temperatures, larvae developed through fewer larval instars. Two dominant developmental pathways were observed; a short pathway of four instars and a long pathway of five instars. Longer developmental pathways of six to seven instars were rarely observed (mostly at lower temperatures) and consisted of additional instars as ‘repeat’ instars; i.e. little developmental advance over the preceding instar. To assess the implications of temperature-mediated variation in larval instar number, newly-hatched larvae were then reared at 15, 20, and 25°C. Again, the proportion of larvae developing through four instars increased with temperature. At all temperatures, larval development time and juvenile dry weight were greater for larvae developing through five instars. Importantly, because of the increasing proportion of larvae developing through four instars with increasing temperature, larval traits associated with this pathway (reduced development time and juvenile dry weight) became more dominant. As a consequence of increasing growth rate with temperature, and the shift in the proportion of larvae developing through four instars, juvenile dry weight was greatest at intermediate temperatures (20°C). We conclude that at settlement P. varians juveniles do not follow the temperature-size rule; this is of importance for life-history ecology in response to environmental change, as well as for aquaculture applications.

Different thermal preferences for brooding and larval dispersal of two neighboring shrimps in deep‐sea hydrothermal vent fields

“…Such thermal effects are commonly observed in shrimps and other marine animals (e.g. Oliphant et al 2013). In some cases, temperature influences reproductive frequency, e.g.…”

Occurrence and predictive utility of isochronal, equiproportional, and other types of development among arthropods

“…This finding is perhaps not so surprising, given that an increasing body of work in recent years has shown that many (and possibly all?) arthropod species exhibit at least some plasticity in their immature developmental pathways (Jarošík et al, 2002, 2004; Oliphant et al, 2013; Karimi-Malati et al, 2014; Quinn, 2016). Many species of decapod crustaceans (e.g., Boyd and Johnson, 1963; Hamasaki et al, 2009) and insects (e.g., Karimi-Malati et al, 2014) develop through additional or alternative stages or instars under suboptimal conditions, such as extreme temperatures, low food supply, presence of contaminants, or limited availability of substrate for settlement (Oliphant et al, 2013; Quinn, 2016 and references therein).…”

“…arthropod species exhibit at least some plasticity in their immature developmental pathways (Jarošík et al, 2002, 2004; Oliphant et al, 2013; Karimi-Malati et al, 2014; Quinn, 2016). Many species of decapod crustaceans (e.g., Boyd and Johnson, 1963; Hamasaki et al, 2009) and insects (e.g., Karimi-Malati et al, 2014) develop through additional or alternative stages or instars under suboptimal conditions, such as extreme temperatures, low food supply, presence of contaminants, or limited availability of substrate for settlement (Oliphant et al, 2013; Quinn, 2016 and references therein). In many cases, such developmental plasticity is thought to be adaptive; for example, at low temperatures the shrimp Palaemon varians LEACH, 1813 (formerly Palaemonetes varians ) develops through 1-3 additional stages at lower temperatures than it does at higher temperatures, which is presumed to allow it to delay settlement to juvenile habitats and give it more time to feed and grow to a larger size before settling (resulting in lower post-settlement mortality) than it otherwise could achieve under low-temperature conditions (Oliphant et al, 2013).…”

“…The specific implications of this form of plasticity are not immediately clear and likely vary on a case-by-case basis, but one can imagine similar outcomes to the occurrence of extra stages. For instance, the lengthening of the last developmental stage at suboptimal temperatures may permit more feeding in preparation for metamorphosis, and thus attaining a larger postmetamorphic size ( sensu Oliphant et al, 2013). The results of the present study strongly suggest that developmental plasticity is a general phenomenon among arthropods, but more research is needed on the exact nature, evolution, and implications of developmental plasticity among arthropod taxa (Quinn, 2016).…”

“…Perhaps some intermediately timed stages might also be less flexible if processes occur during them that are required for later development and successful metamorphosis, as in the second zoea stage of many decapods (Anger 2001; Quinn, 2016). Later stages of crustaceans, which must settle to the benthos before metamorphosing, may also be more plastic due to the possibility of them not encountering suitable substrate immediately when reaching competence (Pineda and Reyns, 2018) or having experienced insufficient growth as larvae to be successful after metamorphosis (Oliphant et al, 2013). Future analyses of such possible features of mixed and VPD types of development will no doubt reveal interesting characteristics of arthropod species.…”