Reproduction
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Research study 1
 

photograph of a sea pen Ptilosarcus gurneyi showing nodes of parasitic isopodsSexes are separate in sea pens Ptilosarcus gurneyi.  The gonads develop within the linings of the compartmentalised digestive cavities of the feeding polyps.  Gametes are released via the polyp mouths in springtime and fertilisation occurs in the open water.  Eggs are about 0.5mm in diameter, orange in colour, and fat-filled.  Development in the lab to a planula larva occurs after 4d at 12OC, and the larvaphotograph of several leaves of a sea pen Ptilosarcus gurneyi showing parasitic isopods, eggs, and details of feeding and respiratory polypsare capable of settling and metamorphosing after 7d.  The larvae are lecithotrophic and thus non-feeding. Chia & Crawford 1973 Mar Biol 23: 73; Chia & Crawford 1977 J Morphol 151: 131.

NOTE  lit. “yolk food” G., referring to the fact that the larvae subsist on yolk for nutrients and energy, and do not feed

Close view of leaves, feeding polyps, and the yellow
swelling of a parasitic isopod. Other features of note
are some damage to 2 leaves, and the possibility that
this individual is gravid, with eggs being visible as
yellow, opaque aggregations at the bases of the
polyps. The siphonozooids, or respiratory polyps are
visible as bumps on the rachis on the Right 1.2X



A single colony of Ptilosarcus gurneyi may produce over 200,000 eggs.
The inflated base is called a peduncle, while the upper part is the rachis
bearing numerous leaves. At the free edges of the leaves are the
autozooids
or feeding polyps, while respiratory
polyps
are visible as 2 darker yellow stripes running
up the rachis. The large bumps seen in the leaves are
not eggs; rather, they are parasitic isopods. 0.4Xphotograph of planula larva of a sea pen Ptilosarcus gurneyi


The planula larva of P. gurneyi is ciliated and swims capably.
The stomodaeum, or presumptive mouth, is visible as a dimple
at the anterior end, on the Left side of the photo


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Research study 2
 
The accompanying photos show different developmental stages of Ptilosarcus gurneyi from a few weeks after metamorphosis to a mature colony.
photograph of a juvenile sea pen Ptilosarcus gurneyi showing details of feeding and respiratory polyps
Note in this young stage the 2 types of polyps: the siphonozooids (respiratory polyps) on either side of the rachis and the autozooids (feediing polyps) at the free edges of the leaves. At this early stage there are only a few polyps on each leaf, with only 4 tentacles each 5X
photograph of a juvenile sea pen Ptilosarcus gurneyi
An older individual, perhaps several months of age, with abundant siphonozooids and a well developed peduncle, or base. Not visible is a slender, proteinaceous supporting rod that runs about one-third the length of the animal from the distal end of the peduncle 0.4X

Close view of the rachis with its many leaves bearing the autozooids or feeding polyps. The digestive or gastrovascular cavities of the feeding polyps extend inwards within the leaves and inter-communicate, thus ensuring nutrient delivery to all parts of the colony 1X
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Research study 3
 

photograph of soft coral Alcyonium sp.Soft corals Alcyonium sp. reproduce both sexually, by release of gametes, and asexually, by clonal fission.  A 2-yr field study employing photographic techniques on 4 populations at Tatoosh Island, Washington reveals that despite high turnover, population densities remain relatively constant.  An average mortality rate of 38% is matched by recruitment of daughter colonies produced by fission.  The author observes no larval recruitment to the populations and notes that sexual reproduction is infrequent.  As colony size increases, mortality decreases and the proportion of colonies reproducing by fission increases. The author develops demographic models to predict fitness, and determines that elimination of sexual reproduction from the life cycle would have only negligible effect on fitness, while elimination of fission would likely lead to extinction.  McFadden 1991 Ecology 72: 1849.schematic showing fates of Alcyonium colonies over a 2-mo period at Tatoosh Island

NOTE  the proportion of colonies reproducing sexually never exceeds 15% for all size classes

 

Right: tracings of photographs of Alcyonium colonies at Tatoosh
Island taken 2mo apart.  Light pink outlines indicate colony positions
in March and darker overlays indicate the same colonies in May. 
Note how some of the colonies have crawled around (m = move),
some have split apart (f = fission), while others have died (d = dead)

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Research study 4
 

photograph of clones of soft coral Alcyonium sp.Reproduction predominantly by asexual fission leading to daughter clones that move relatively little, as in Alcyonium sp., should lead to pronounced small-scale genetic structure.  Tests of this in a population of Alcyonium sp. at Tatoosh Island, Washington, however, by researchers from Harvey Mudd College, Claremont generally no show significant small-scale genetic structure among individuals separated by up to 40m.  The authors suggest that maintenance of close spacing between clonemates may increase their feeding efficiency; therefore, limited dispersal of the asexual units is selectively advantageous.  Such clones are thought to live for decades.  McFadden & Aydin 1996 Mar Biol 126 (2): 215.

NOTE  analysis of 5 allozyme loci in both individuals and clones, using spatial-autocorrelation analysis-techniques

 

 

Numerous growths of Alcyonium sp., some possibly
clones, interspersed among Cribrinopsis anemones in
the cold, clear water of northern Vancouver Island 0.4X

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