Geologic significance of coiling direction in the planktonic foraminifera Pulleniatina

Saitō, Tsunemasa

doi:10.1130/0091-7613(1976)4<305:gsocdi>2.0.co;2

Cited by 119 publications

(128 citation statements)

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“…Clear evidence for allopatric speciation following this uplift has been obtained for a number of benthic marine groups (e.g., Woodring 1966;Herm 1969;Crouch and Poag 1979;Lessios 1981;Vermeij 1987;Cronin and Ikeya 1990). The rise of the isthmus may explain the different stratigraphic ranges of several planktonic foraminifer taxa on the Atlantic versus Pacific side beginning three to four million years ago (Parker 1973;Saito 1976;Keigwin 1982;Pearson 1995;Cronin and Dowsett 1996). Incongruence in these planktonic foraminifer distributions is probably related to changes in watermass conditions as well as to segregation of planktonic foraminifer gene pools following the isthmus uplift.…”

Section: Speciation Processmentioning

confidence: 99%

Cryptic speciation in the living planktonic foraminiferGlobigerinella siphonifera(d'Orbigny)

1997

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Abstract.-Two living forms of Globigerinella siphonifera (d'Orbigny), presently identified as Type I and Type II, can easily be distinguished and collected by SCUBA divers because of differences in appearance, arrangement of the rhizopodial network, and the presence or absence of commensals. Additional biological differences are apparent from laboratory culture experiments; Type I individuals survive significantly longer than Type II under conditions of darkness and starvation and have significantly slower chamber formation rates. Stable isotopic analyses of Types I and II also reveal notable differences, with Type I consistently yielding more negative S'^O and 8"C values. Results of Mg / Ca ratio analyses indicate that Type II specimens precipitated their shells in slightly cooler (deeper) surface waters than Type I specimens. These observations and results from DNA sequencing unequivocally demonstrate that G. siphonifera Types I and II should be regarded as biological sister species.Contrarily, biometric analysis of the empty shells reveals few significant differences between G. siphonifera Types I and II. Of all the features measured from X-ray and SEM images of serially dissected specimens, only shell porosity yields readily discernible differences, with Type I adult chambers averaging 10-20% porosity and Type II adult chambers averaging 4-7% porosity. Statistically significant differences between Type I and II populations are revealed in maximum test diameter (Type I is typically larger) and coiling (Type I is typically more evolute), but these differences do not justify species level distinction of Types I and II using traditional paleontological species concepts.On the basis of the above evidence, and since all specimens were collected at the same location at ~ 3-8 m water depth, we conclude that G. siphonifera Types I and II are living examples of cryptic speciation, whereby biological speciation has occurred in the absence of discernable change in shell morphology. However, it is not clear when or where this speciation took place. Preliminary study of deep-sea cores from the Caribbean and Pacific sides of the Isthmus of Panama reveals a predominance of specimens with Type II porosity values, with rare occurrence of specimens yielding Type I porosity values. Systematic downcore measurement of shell porosity and tightness of coiling needs to be extended back to the middle Miocene, when G. siphonifera first appeared, to determine the timing of the Type I and II morphological divergence.Postulated mechanisms for reproductive isolation and speciation of Types I and II include alloparapatric, depth parapatric, and sympatric speciation. These models could be tested if further analysis of fossil G. siphonifera shells allows determination of the timing of speciation, the preferred depth distribution, and the history of geographic distribution of Types I and II.

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Section: Speciation Processmentioning

confidence: 99%

Cryptic speciation in the living planktonic foraminiferGlobigerinella siphonifera(d'Orbigny)

1997

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“…Results of these two months (Fig. I) suggest that in 1982, as in 1976-1977, the two species are ready to spawn in September but not in June. The September data also suggest that D. mexicanum spawns during the third lunar quarter, with a peak 3-4 days after full moon, while D. antillarum spawns in the first lunar quarter, with a peak 1-2 days after new moon.…”

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confidence: 99%

“…The Isthmus ofPanama is a geographic feature that fulfills these conditions. Connections between the tropical Atlantic and Pacific oceans were severed in the Pliocene, 3.1 to 3.5 million years ago (Saito, 1976;Keigwin, 1978Keigwin, , 1982. The separation between previously continuous marine populations has resulted in a host of "geminate species," i.e., closely related species, one on each side of Central America (Jordan, 1908;Ekman, 1953).…”

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confidence: 99%

Possible Prezygotic Reproductive Isolation in Sea Urchins Separated by the Isthmus of Panama

Lessios

1984

Evolution

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“…The separation of Caribbean and eastern Pacific populations by the rise ofthe Central American Isthmus 3.0 to 3.5 mya (Saito 1976;Keigwin 1978Keigwin , 1982Coates et al 1992) provides a fixed historical point at which gene flow between populations was severed. The existence of distinct morphotypes in E. braziliensis and of a closely related species ofExcirolana also provides points of possible historical branching.…”

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confidence: 99%

GENETIC AND MORPHOLOGICAL DIVERGENCE AMONG MORPHOTYPES OF THE ISOPOD EXCIROLANA ON THE TWO SIDES OF THE ISTHMUS OF PANAMA

Lessios

Weinberg

1994

Evolution

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Abstract. -Excirolana braziliensis is a dioecious marine isopod that lives in the high intertidal zone of sandy beaches on both sides of Central and South America. It possesses no larval stage and has only limited means of adult dispersal. Indirect estimates of gene flow have indicated that populations from each beach exchange less than one propagule per generation. Multivariate morphometrics have discovered three morphs of this species in Panama, two of them closely related and found on opposite sides of Central America ("C morph" in the Caribbean and "C' morph" in the eastern Pacific), the third found predominantly in the eastern Pacific ("P morph"). Though the P and C' morphs are seldom found on the same beach, they have overlapping latitudinal ranges in the eastern Pacific. A related species, Excirolana chamensis, has been described from the Pacific coast of Panama. Each beach contains populations that remain morphologically and genetically stable, but a single drastic change in both isozymes and morphology has been documented. We studied isozymes and multivariate morphology of 10 populations of E. braziliensis and of one population of E. chamensis. Our objective was to assess the degree of genetic and morphological variation, the correlation of divergence on these two levels of integration, the phylogenetic relationships between morphs, and the possible contributions of low vagility, low gene flow, and occasional extinction and recolonization to the genetic structuring ofpopulations. Genetic distance between the P morph, on one hand, and the other two morphotypes ofE. braziliensis, on the other, was as high as the distance between E. braziliensis and E. chamensis. Several lines of evidence agree that E. chamensis and the P morph had diverged from other morphs of E. braziliensis before the rise of the Panama Isthmus separated the C and C' forms, and that the P morph constitutes a different species. A high degree of genetic differentiation also exists between populations of the same morpho On the isozyme level, every population can be differentiated from every other on the basis of at least one diagnostically different locus, regardless of geographical distance or morphological affiliation. Morphological and genetic distances between populations are highly correlated. However, despite the high degree of local variation, evolution of E. braziliensis as a whole has not been particularly rapid; divergence between the C and C' morphs isolated for 3 million yr by the Isthmus of Panama is not high by the standard of within-morph differentiation or by comparison with other organisms similarly separated. Alleles that are common in one population may be absent from another of the same morph, yet they appear in a different morph in a separate ocean. The high degree oflocal differentiation, the exclusive occupation ofa beach by one genotype with rare arrival offoreign individuals that cannot interbreed freely with the residents, the genetic stability of populations with infrequent complete replacement by another genetic...

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Geologic significance of coiling direction in the planktonic foraminifera Pulleniatina

Cited by 119 publications

References 0 publications

Cryptic speciation in the living planktonic foraminiferGlobigerinella siphonifera(d'Orbigny)

Cryptic speciation in the living planktonic foraminiferGlobigerinella siphonifera(d'Orbigny)

Possible Prezygotic Reproductive Isolation in Sea Urchins Separated by the Isthmus of Panama

GENETIC AND MORPHOLOGICAL DIVERGENCE AMONG MORPHOTYPES OF THE ISOPOD EXCIROLANA ON THE TWO SIDES OF THE ISTHMUS OF PANAMA

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