An ecological genetic analysis of the settling behaviour of a marine polychaete:

We conducted still-water time-course experiments on cultured larvae of the serpulid polychaete Hydroides dianthus (Verrill, 1873) to examine timing and patterns of gregarious and nongregarious settlement to better understand the conditions under which larvae of a gregarious species colonize new habitats. We first confirmed that these worms are aggregated in the field, and quantified patterns of association with a number of other common intertidal species. Patterns of negative association with spatial competitors is unlikely to have resulted from larval avoidance during settlement, because we found no difference in larval settlement in response to conspecifics with or without the solitary tunicate Ascidia interrupta present. We then examined the settlement of competent larvae in response to biofilm and conspecifics to determine the conditions under which the larvae of this gregarious species settle nongregariously. Larvae settled concurrently in response to both biofilm and conspecifics, starting approximately 4 d after fertilization, and response was of similar magnitude to both biofilm and to conspecifics for the first couple of days post-competency. While settlement in response to conspecifics continued in subsequent assays carried out over 70 d (at which time larvae began to die in culture), settlement in response to biofilm decreased abruptly after the peak, and ceased by Day 14. Settlement patterns were qualitatively similar regardless of previous exposure to substrata; similar results were obtained whether the whole population of larvae in culture was denied access to or daily provided access to 1 or both experimental substrata. Furthermore, these patterns of settlement did not change as larval planktonic period was prolonged. Of larvae settling during 24 h sample assays, the majority of larvae metamorphosed in response to biofilm during the first 6 h, whereas metamorphosis in the final 6 h (between 18 and 24 h) of the assays was primarily in response to conspecifics. These results are opposite to the pattern predicted by the desperate larva hypothesis, because some larvae settled in response to biofilm even after rejecting conspecifics the previous day. In fact, cultures of competent larvae appear to become more specific in terms of larval settlement in response to live adult conspecifics as the planktonic period is artificially prolonged.

Section: Discussionmentioning

confidence: 98%

Settlement of the gregarious tube worm Hydroides dianthus (Polychaeta: Serpulidae). I. Gregarious and nongregarious settlement

Toonen¹,

Pawlik²

2001

“…and gregariously in response to conspecific juveniles, while larvae from an exposed population settled on Fucus spp. and were not gregarious (Mackay & Doyle 1978). Cyprid larvae of a specialist barnacle settled either on the exposed axial skeleton of gorgonian corals or on adult conspecifics, ensuring proximity to mates for some larvae (Gomez 1973).…”

Section: Variation In Dispersal Potential Among Sibling Larvaementioning

confidence: 99%

Bet-hedging dispersal strategy of a specialist marine herbivore: a settlement dimorphism among sibling larvae of Alderia modesta

Krug¹

2001

Dispersal polymorphisms are known from many terrestrial organisms that inhabit fluctuating environments, but they are not well-recognized among marine invertebrates. An unusual form of variation was found in the settlement behavior of lecithotrophic larvae of the mollusc Alderia modesta (Lovén, 1844) that markedly altered the dispersal potential of sibling larvae. Most clutches contained, in variable proportions, larvae that spontaneously metamorphosed in the egg mass or within 2 d of hatching, and larvae that delayed metamorphosis until encountering the obligate adult food, the yellow-green alga Vaucheria longicaulis. The proportion of larvae undergoing spontaneous metamorphosis within a clutch was highly variable, ranging from 0 to 90%, and was unrelated to adult size. The proportion of intracapsular metamorphosis was also variable, ranging from 0 to 32%. The percentage of spontaneous metamorphosis per clutch was phenotypically plastic: when adults were starved, there was a significant tendency for each successive clutch to have a lower percentage of spontaneous metamorphosis, thus increasing the dispersal potential of the offspring. The decrease in spontaneous metamorphosis was significant after only 24 h of starvation. There was no significant increase in the cumulative level of spontaneous metamorphosis after the 2nd day post-hatching, but larval mortality increased as a linear function after the 5th day. Most larvae that did not spontaneously settle in the first 2 d delayed metamorphosis until they were exposed to the adult host alga, V. longicaulis. When 2 d old larvae were exposed to 17 species of macroalgae and sediment from the adult habitat, only V. longicaulis induced significant metamorphosis (93.3 ± 6.7%); all other species of algae and field sediment induced no metamorphosis or low levels (0-9%) that were not significantly higher than sea water controls. There was no difference in the settlement specificity of 2 and 9 d old larvae when tested against 2 different algae, nor in their ability to complete metamorphosis. The high initial percentage of spontaneous metamorphosis reduces the dispersal potential of some larvae in each clutch relative to their siblings that delay metamorphosis until stimulated by V. longicaulis; this settlement dimorphism represents a novel bet-hedging strategy among marine invertebrates.

“…Metamorphosis of larvae of spirorbid polychaetes in response to algal substrata (Knight-Jones et al 1971, Doyle 1976, MacKay & Doyle 1978, gregarious attachment of the bryozoan Bugula neritina (Raimondi & Keough 1990) and the polychaete Hydroides dianthus (Toonen & Pawlik 1994), response of cyprids of the barnacle Semibalanus balanoides to crevices (Chabot & Bourget 1988), and sensitivity of veligers of Phestilla sibogae to a coral inducer (Hadfield 1984), all exhibit genetic variation or differences among populations suggestive of genetic variation. The environment in which larvae develop may affect the ability to detect or respond to a settlement cue.…”

Section: Introductionmentioning

confidence: 99%

Variation in attachment of the barnacle Balanus amphitrite: sensation or something else?

Holm¹,

McClary²,

Rittschof

2000

Settlement, attachment, and metamorphosis of larvae of marine invertebrates is extremely variable in the laboratory and in nature. The relative contributions of genetic, ontogenetic and environmental effects to this variation are not well understood. We tested for genetic, maternal and ontogenetic effects on permanent attachment of cyprids of the barnacle Balanus amphitrite (Darwin). Larvae were assayed for attachment in response to a control treatment and 3 artificial inducers: 20-hydroxyecdysone (20-HE), 3-isobutyl-1-methylxanthine (IBMX), and phorbol 12,13-dibutyrate (PDB). We observed strong family effects on attachment in the control, 20-HE, and IBMX treatments, suggesting that attachment in response to these treatments is influenced by genetic or maternal factors. In addition, attachment responses were correlated, indicating that the same genetic or maternal factors may affect attachment in each treatment. Family effects on attachment in the control treatments decreased with cypris age, suggesting the loss of genetically-or maternallyinfluenced discriminatory behavior in older larvae. The mechanisms underlying genetic or maternal effects on attachment may act via the external receptors and signal-transduction pathways regulating larval responses. Alternatively, there may be variation in larval 'vigor' or the rate at which cyprids attain metamorphic competence.