FLEMINGER and HULSEMANN: FOUR SIBLING SPECIES OF PONTELLINA 



REMARKS ON SEASONAL 

 OCCURRENCE AND BREEDING 



Captui'e records alone do not necessarily dis- 

 close the distribution of the optimal habitat of a 

 planktonic species (Fleminger, 1972), i.e., 

 the region in which reproduction is usual, 

 typically successful, and from which the progeny 

 is likely to become entrained in a circulation 

 system that ultimately provides new breeding 

 stocks with suitable conditions for their off- 

 spring. Our sampling of PoiiteUiua is incomplete 

 for critical assessment of the impact of seasonal 

 change on occurrence, geographical distribu- 

 tion, or reproduction. Moreover, as a conse- 

 quence of the relatively large mesh sizes of the 

 nets (see Table 15) sampling of most juvenile 

 stages was not representative. Thus spermato- 

 phore occurrence on females is the only source 

 of breeding information available to us. 



In C«/o»».s\ spermatophores constitute evi- 

 dence of mating within the past 48 h (Marshall 

 and Orr, 1955). In other copepods, spermato- 

 phores are lost or shed soon after attachment; 

 in Labidocera trispiitosa discarding of the 

 spermatophore has been observed to occur just 

 prior to egg laying (G. Theilacker, pers. comm., 

 1970). 



Few spermatophores were observed in Poiitel- 

 Uiia (Table 5) suggesting that as in Calanus 

 they are not retained for an appreciable time 

 after attachment. The 27 records of s(>b)i)ia 

 females bearing a spermatophore afford a 

 glimpse of breeding patterns in that species. 

 Spermatophore-bearing females appeared in 

 Febi-uary, May, and August samples. The local- 

 ities span most of the latitudinal extent of 

 sobrina captures on record, but all lie to the 

 east of long. 98°W, and most are relatively close 

 to the mid-American coast. In contrast, the few 

 records of morii and plionata bearing spermato- 

 phores are widespread, suggesting that both 

 species breed over a more extensive range in 

 accordance with their more extensive geographi- 

 cal distributions. 



PHYLOGENETIC 



RELATIONSHIPS AMONG 



THE PONTELLINA SIBLINGS 



Dobzhansky (1972) stressed the heuristic 

 value of sibling species when he pointed out 



"... sibling species permit the dissection of 

 the process of speciation into studiable com- 

 ponents." PoiitelUna appears especially well 

 suited to explore the question of speciation in 

 the planktonic biotope. Restriction to shallow 

 tropical and subtropical oceanic waters apparent- 

 ly limits opportunities for complex diversity 

 in i)lanktonic calanoids (Fleminger and Hulse- 

 mann, 1973). The four species of Po)itelli)ia 

 satisfy the number of suitable ranges that appear 

 to be available within these biogeographical 

 limits. 



Three of these ranges reflect the geographical- 

 ly limited and relatively shallow lenses of 

 Tropical Surface Water (Wyrtki, 1966, 1967) 

 described from the eastern equatorial Pacific 

 but also known on the basis of similar general 

 features to prevail in the equatorial Atlantic 

 Ocean (Muromtsev, 1963) and in the equatorial 

 Indian Ocean (Wyrtki, 1971). The fourth range 

 consists of the series of deeper lenses of warm 

 water beyond Tropical Surface Waters and 

 lying between the subtropical convergences in 

 the Atlantic, Indian, and Pacific Oceans. 



PonteUiiia's position as a distinctive genus 

 is unchallenged, being strongly separated 

 from its closest relative, P(>)tteUopsis, in both 

 morphology and habitat. Compelling evidence 

 favoring consideration of the four populations 

 of P(>)iteUi)ia as separate species is furnished 

 by the morphological distinctions of each, their 

 independent geographical distributions, and 

 the morphological integrity of their diagnostic 

 features. That is, despite widespread regions of 

 geographical overlap where two or three of the 

 species may be captured in the same net tow, 

 no evidence of intergradation or hybridization 

 has been observed. 



Evidence of strongly regionalized habitat 

 adaptation may be inferred from the apparent 

 failure of each species to colonize areas occupied 

 by its adjacent congener. Failure to colonize 

 must be regarded as significant. All four species 

 occur in surface layers (Wilson, 1942; Heinrich, 

 1961; Vinogradov and Voronina, 1964; Flemin- 

 ger and Hulsemann, unpublished data) where 

 air-sea interactions provide opportunity for 

 dispersal and advection with neighboring cir- 

 culation systems, but the distribution of each 

 species overlaps at most only a portion of the 

 range of its neighboring congeners. 



93 



