Reproduction & development
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  Larval cloning & regeneration
  Topics relating to reproduction & development include laval cloning & regeneration, considered here, and SELECTED GENERA, EGG SIZE & ENERGY CONTENT, and TO BROADCAST SPAWN OR BROOD?, presented in other sections.
 

photograph of ochre star Pisaster ochraceus with a split arm
Although regeneration in adult sea stars is known in many species, little work has been done on the phenomenon in the larvae.

 

 




 

Ochre star Pisaster ochraceus regenerating
a portion of arm tip perhaps from damage 1X

 
Research study 1
 

photograph of a bipinnaria larva of Pisaster ochraceus showing cut line used in studies of regenerationIn the first study of its kind, researchers at Friday Harbor Laboratories surgically bisect Pisaster ochraceus bipinnaria1 and brachiolaria lavae, and observe that both halves regenerate completely in 12-14d2 (see photo on Right and photo series below). Despite removal of the mouth and esophagus, the posterior half of the larva at Day1 is able to capture and ingest phytoplankton particles.  However, feeding by the anterior larva does not commence until Day7, following regeneration of the digestive organs and coelom. Note that by Day12 both anterior and posterior larvae have completely regenerated and, by Day14, are essentially indistinguishable from control larvae.

Given that the surgical bisection may simulate natural damage to the larvae during its stay in the plankton, the authors suggest that population models incorporating past data on larval mortality may be using mortality estimates that are unrealistically high.  The authors note that their study is the first on regeneration of lost body parts requiring organogenesis in a metazoan larva3Vickery & McClintock 1998 Nature 394:140; for a detailed review of regeneration in echinoderm larvae see Vickery et al. 2001 Microsc Res Tech 55: 464.

NOTE1  bipinnaria of the sea star Luidia foliata are also used with similar results sd those for the ochre star

NOTE2  culture temperature is not given

NOTE3  do the authors actually mean “invertebrate metazoan larva”? Much work on regeneration in amphibian larvae has been done

   
  The photo series below shows the developmental timeline for the regenerating larvae:
 
Anterior part: photograph of the 2 halves of a bipinnaria larva of Pisaster ochraceus surgically cut 1d previously
photos of 2 halves of a bipinnaria larva of the sea star surgically cut 3d previously

photos of 2 halves of a bipinnaria larva of the sea star surgically cut 7d previously
photos of 2 halves of a bipinnaria larva of the sea star surgically cut 9-10d previously
photos of 2 halves of a bipinnaria larva of the sea star surgically cut 12d previously
Posterior part:
  Day 1: the posterior part is able to feed Day 3-4: the larval pieces have elongated along their A-P axes Day 7: the anterior regenerating part is now able to feed Day 9-10: ciliary bands have regenerated in both the anterior and posterior larvae Day 12: larvae are functional entities
 
Research study 2
 

photograph of a bipinnaria larva of an ochre sea star Pisaster ochraceus forming a clonal larval bud
graph showing growth & survival of larvae of ochre stars Pisaster ochraceus on different rationsIt has long been known that sea-star larvae can clone themselves but, until recently, the factors regulating this were not well understood.  A clone originates as a small bud on a mature bipinnaria larva and this soon detaches and develops into another bipinnaria larva (see photo on Left). The experiments described here involve culturing larvae of ochre stars Pisaster ochraceus at the Friday Harbor Laboratories, Washingtn under 9 combinations of 3 temperatures1 and 3 food concentrations2.

Results show that larvae at the medium histograms showing % larvae of ochre stars Pisaster ochraceus undergoing cloning especially at the competent brachiolaria stage on high rations at intermediate culture temperaturestemperature and on the highest ration grow fastest (see graph upper Right). These larvae produce the most clones. Most cloning occurs after the onset of the brachiolaria stage (see histogram lower Right).  All larvae die in the high-temperature treatments and those in the low-temperature treatment fail to attain the brachiolaria stage. In another experiment, larvae fed on a mixed diet of phytoplankton grow more and produce significantly more clones than ones fed on monospecific3 diets.

The clones develop normally and after about 2wk they are functionally and morphologically indistinguishable from larvae in the cultures from which they originate.  The authors conclude that production of most clones under conditions of optimal temperture and food may serve to increase larval populations when the environment is most conducive to larval growth.  Vickery & McClintock 2000 Biol Bull 199: 298.

NOTE1 low: 7-10oC, medium: 12-15 oC, and high: 17-20oC; only results for the intermediate treatment are shown here

NOTE2  5x102, 5x103, and 5x104 cells . ml-1, of an equal mix of diatoms Chaetocerous calcitrans, and 2 flagellates Dunaliella tertiolecta and Isochrysis galbana

NOTE3  growth of larvae on Isochrysis galbana seems the same as on a mixed diet, suggesting that this species may represent the major nutritional contribution of the 3 species in the mixed diet

 
Research study 3
 

drawing series showing stages in organogenesis in regenerating bipinnaria larvae of an ochre star Pisaster ochraceus following surgical bisectionphotos showing a bipinnaria larva of an ochre star Pisaster ochraceus with a tip of a brachiolar arm removed surgicallyA later study by the same research group at Friday Harbor Laboratories provides further details of regenerative capacity and process in sea-star larvae, most notably, those of Pisaster ochraceus.  Surgically bisected bipinnaria larvae (21d of age) show the progression of organogenesis in the anterior half as shown in the drawings on the Left. Note that no part of the coelomic pouches remain after bisection and these later form as lateral evaginations of the newly formed digestive system. 

If arm tips or whole arms are removed they survive for over 2wk and swim about, but never regenerate (see photos on Right). The larva itself will regenerate the missing arms but posterolateral arms never seem to attain the same length as before. Vickery et al 2002 Biol Bull 203: 121.

NOTE  the authors provide information on regeneration in west-coast sea stars Luidia foliata and sand dollars Dendraster excentricus, but only information on the ochre star is considered here

 
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