Three sibling species of didemnid ascidians from northern Norway: Didemnum albidum (Verrill, 1871), Didemnum polare (Hartmeyer, 1903), and Didemnum romssae sp.nov.

1996 ◽  
Vol 74 (2) ◽  
pp. 357-379 ◽  
Author(s):  
Jessica A. Marks
Keyword(s):  
Life History ◽  
Sibling Species ◽  
Distinct Species ◽  
Morphological Characters ◽  
Reticulate Evolution ◽  
Life History Variation ◽  
Larval Size ◽  
Colonial Ascidian ◽  
Northern Norway ◽  
Didemnid Ascidians

Recent advances in taxonomy have disclosed the prevalence of cryptic sibling species in marine systems. In didemnid ascidians, morphological variation between species is often slight, and many species may have been overlooked. Species boundaries within this group are often equivocal, and patterns among taxa are reminiscent of those formed by reticulate evolution in plants. Specimens of the sessile colonial ascidian Didemnum albidum (Verrill, 1871) were examined for life-history and morphological characters and found to constitute at least three sympatric sibling species. One of these, Didemnum romssae, is described here as a new species. Colonies were collected from hard-bottom assemblages in Troms and Finnmark counties in northern Norway. Zooid morphology in D. romssae is similar to that of D. albidum, but varies within each species, even for traits usually considered specific. Didemnum romssae is proposed as a distinct species on the basis of consistent differences in (i) the shape and size of calcium carbonate spicules within the common test; (ii) larval size and the number of lateral ampullae; (iii) timing of reproduction; and (iv) the absence of a seasonal nonfeeding, overwintering stage, which occurs in D. albidum. Examination of specimens from museum collections considered synonymous with D. albidum confirmed the presence of a third species, Didemnum polare (Hartmeyer, 1903), which differed from the other two species in zooid and larval morphology as well as spicule shape. Complexes of sibling species such as these provide a tractable system for studying the consequences of life-history variation among closely related taxa.

Egg size and taxon: their influence on survival and development of chrysopid hatchlings after food and water deprivation

1991 ◽  
Vol 69 (10) ◽  
pp. 2644-2650 ◽  
Author(s):  
Catherine A. Tauber ◽  
Maurice J. Tauber ◽  
Michael J. Tauber
Keyword(s):  
Life History ◽  
Water Deprivation ◽  
Egg Size ◽  
Maternal Investment ◽  
Developmental Rate ◽  
Life History Variation ◽  
Larval Size ◽  
First Instar ◽  
Survival And Development ◽  
Phylogenetic Lineages

Genus- and species-level differences characterize the pattern of life-history variation in two distinct phylogenetic lineages of chrysopids, Chrysopa and Chrysoperla. Species in the genus Chrysopa exhibit significant variation in egg size, and this variation is positively correlated with the ability of hatchlings to withstand periods of food and water deprivation prior to their initial feeding. The variation is also significantly correlated with larval size, as measured by the tibial length of first-instar larvae. Although the six Chrysopa species differ in several other life-history traits (i.e, the incubation period and rate of first-instar larval development), the variation is unrelated to egg size. It appears that maternal allocation of resources to eggs largely serves to enhance embryonic growth and the survival of hatchlings during searching. That is, within the Chrysopa lineage egg size varies; larger eggs yield larger, more robust hatchlings. These hatchlings may or may not develop faster than congeners from small eggs. In comparison with Chrysopa, the genus Chrysoperla has less variability in egg size and developmental rate. Furthermore, although Chrysoperla eggs are relatively small, the ability of hatchlings to endure periods of food or water deprivation is at least as great as it is in the Chrysopa species with large eggs. We conclude that maternal investment in larval fitness has different ontogenetic pathways, ecological roles, and phylogenetic histories in the two genera.

Coral biodiversity and evolution: recent molecular contributions

2002 ◽  
Vol 80 (10) ◽  
pp. 1723-1734 ◽  
Author(s):  
Uri Frank ◽  
Ofer Mokady
Keyword(s):  
Life History ◽  
Life History Traits ◽  
Recent Literature ◽  
Morphological Characters ◽  
Reticulate Evolution ◽  
The Past ◽  
Tropical Reefs ◽  
New Concepts ◽  
Molecular Studies ◽  
The Subject

Tropical reefs are among the most diverse ecosystems. Corals, as the most prominent members and framework builders of these communities, deserve special attention, especially in light of the recent decline of coral reefs worldwide. The diversity of corals at various levels has been the subject of many studies, and has traditionally been investigated using morphological characters. This approach has proved insufficient, owing to several ecological and life-history traits of corals. The use of molecular/biochemical approaches has been propelling this discipline forward at an ever-increasing rate for the past decade or so. Reticulate evolution in corals, which has challenged traditional views on the ecology, evolution, and biodiversity of these organisms, is only one example of the results of molecular studies supporting the development of new concepts. We review recent literature reporting studies of the biodiversity, ecology, and evolution of corals in which molecular methods have been employed. We anticipate that in the coming years, an increasing number of studies in molecular biology will generate new and exciting ideas regarding the biology of corals.

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