Size Morphs Research Articles

Shared Preferences by Predators and Females for Male Ornaments in Swordtails

Sexually dimorphic traits in many mate recognition systems have evolved in response to preexisting female biases. These biases are often quite general in form and are likely to be shared by predators, thereby imposing a cost on male trait expression. The Mexican tetra Astyanax mexicanus (Pisces: Characidae), a visual predator of swordtail fishes, exhibits the same visual preferences for male body size morphs as do females. Furthermore, tetras in populations where swordtails are absent prefer males with sword ornaments over males with swords removed. The predator preference is thus likely to have arisen prior to contact with fishes bearing the ornament, as has also been suggested for mating preferences for swords.

The effect of mate choice on speciation in snow petrels

Although snow petrels, Pagodroma nivea, show a tendency to assortative mating by size morph, the existence of mixed pairs producing viable young reveals that reproductive isolation between the two size morphs is imperfect. However, the degree of isolation depends on breeding locality. A given area can harbour either (1) only small birds, or (2) only large birds, or (3) small bird colonies close to large bird ones, or (4) mixed pairs, the percentage of which varies from one locality to another. We investigated the mating and nesting patterns that result in mixed pairings and can explain the speciation process considered to be in progress by modern authors. Data from a 34-year demographic study in Terre Adélie, Antarctica, showed that mate and nest fidelity were very high. Nest changes, but not divorces, generally led to higher fecundity. Snow petrels did not seem to choose their mates on the basis of age or experience, and divorcees tended to form new pair bonds with neighbours; nevertheless, there was evidence for active mate fidelity. Pairs involving mates of the same size morph and mixed pairs had similar fecundity. Despite its heterogeneity, the breeding habitat of snow petrels was relatively predictable. Ice repeatedly made some nests unsuitable for breeding. Obtaining a nest that was not frozen was therefore the primary requirement for breeding. Strong competition for nests may explain high fidelity rates and, combined with the absence of reproductive costs in mixed pairs, may have promoted decreased choosiness during mate choice, preventing total reproductive isolation between the two morphs.

Redescription of Neotermes mona, a Dampwood Termite (Isoptera, Kalotermitidae) from the Central West Indies

The winged imago of Neotermes mona (Banks) is described for the first time and the soldier caste is redescribed as two size morphs. The distribution of N. mona includes Hispaniola, Turks & Caicos Islands, Puerto Rico, and Virgin Islands. It is the largest kalotermitid in this region.

Male polymorphism in Limia perugiae (Pisces: Poeciliidae).

The male-polymorphic poeciliid fish, Limia perugiae, a small teleostean endemic to the southeast of the Caribbean island Hispañola, consists of three male size morphs with uniform females. Large males differentiate at a size varying between 25 and 38 mm; intermediate males, between 21 and 25 mm. Under competition, large males exhibit an elaborate courtship display, whereas small males show only a sneak-chase behavior. Intermediate males adapt their tactics to the respective competitors. However, all male morphs can switch from courtship display to sneak-chase behavior. In large mating groups with four males of different size and five or six virgin females, large dominant alpha-males as well as small subordinate delta-males did not produce any offspring. Unexpectedly, all progeny were sired exclusively by the intermediate subordinate beta- and gamma-males. Breeding experiments with the three male morphs can best be explained by a model of Y-linked genes for small and large size which are both suspended by the activity of an autosomal recessive repressor responsible for the development of intermediate males. The dominant allele of the recessive repressor, in either its homoorits heterozygous state, activates the Y-chromosomal genes for large or small size, respectively. Accordingly, intermediate males may produce male offspring of all size classes, depending on the presence of either the Y-linked gene or the autosomal repressor.

Palynological and cytological observations in SpanishSonchus(Asteraceae)

Abstract The pollen morphology of the amphiploid species Sonchus oleraceus L. and its putative parents Sonchus tenerrimus L. and Sonchus asper (L.) Hill is investigated. The related taxa Sonchus microcephalus Mejias, probably derived from S: oleraceus, is also included. S. tenerrimus and S. asper mainly show 3-zonocolporate pollen and no significant differences in size and ornamentation have been detected between them. In S. oleraceus and S. microcephalus, 3- and 4-zonocolporate pollen can be found in the same sample, in very variable proportions, depending on the population; in addition, two different size morphs have been detected in some samples of S. oleraceus. It is proposed that the phenomenon reflects the chromosomal constitution in those species with an amphiploid origin.

Genetic and Morphological Differentiation between Dwarf and Normal Size Forms of Lake Whitefish (Coregonus clupeafotmis) in Como Lake, Ontario

Normal and dwarf size forms of lake whitefish (Coregonus clupeaformis) from Como Lake, Ontario, were sampled at spawning time and examined for differences in electrophoretic, mtDNA, and morphological characteristics to test the hypothesis of reproductive isolation and provide clues regarding evolutionary origin. Of the 36 enzyme loci examined, 33 were fixed for the same alleles in both dwarf and normal lake whitefish. At the three polymorphic loci, allele frequencies were not statistically different between dwarfs and normals. mtDNA analysis revealed five different haplotypes. The same mtDNA haplotype was the most common in both dwarf and normal lake whitefish, but there was a statistically significant difference in haplotype frequencies between the two size forms. Discriminant and principal component analyses demonstrated highly significant morphological differences between dwarfs and normals. Because the two size morphs spawn in the same place at the same time, it is most likely that genetic differences, not different rearing environments, underly the observed morphological differences. mtDNA haplotypes derived from both the Mississippi and Atlantic glacial refugia are present in Como Lake lake whitefish, raising the possibility of an allopatric divergence for the two forms; however, this hypothesis requires testing by genetic comparisons of other sympatric populations in Ontario.

Sympatric Sibling Species Within the Genus Acartia (Copepoda: Calanoida): a Case Study From Westernport and Port Phillip Bays, Australia

ABSTRACT In Westernport and Port Phillip Bays, Victoria, Australia, copepods previously identified as Acartia clausi Giesbrecht or Acartia tranteri Bradford form polymodal length-frequency distributions at some times of the year. The three size morphs of Acartia (large, medium, and small) closely resemble each other in characters other than size. Allozyme electrophoresis of medium and large morphs demonstrated that fixed gene differences occur between these morphs, confirming their diagnosis as separate species. Using comparative morphometrics, we provide taxonomic notes on A. tranteri sensu stricto, describe each of the large and small morphs of Acartia from Victoria, and describe the medium morph as a new species, Acartia fancetti. This new species exhibits morphological variability in size and pigmentation, depending on habitat.

Calanoid copepods from South Georgia, with special reference to size dimorphism within the genus Pseudoboeckella

Three species of calanoid copepods, Boeckella michaelseni, Parabroteas sarsii and Pseudoboeckella poppei were recorded from 6 freshwater localities in the Husvik area, South Georgia. Of the latter species two distinct size morphs occurred, with no overlap in size even in closely situated populations. The large morph was recorded in lakes, the small was found in ponds. The small morph did not coexist with the large predatory P. sarsii, and we suggest predation pressure from this species as the major cause for the observed distribution of these morphs. The pronounced size segregation as well as small morphological dissimilarities suggest that these morphs are reproductively isolated. While the large morphotype corresponds to that of P. poppei, the taxonomic affinities of the small morph are uncertain.

Size and fecundity in the Jamaican gall‐midge Asphondylia boerhaaviae

ABSTRACT. 1. The gall‐midge Asphondylia boerhaaviae Möhn galls weeds belonging to the Nyctaginaceae in Jamaica and other parts of the Caribbean. The species breeds throughout the year with a generation length of < 1 month.2. In adult females, plots of wing length on hind tibial length, of maximum potential fecundity (m.p.f.) on wing length, and of m.p.f. on ovariole number, suggested the presence of a small morph, which the use of discriminant function analysis and other investigations confirmed. There was also good evidence of two size morphs in adult males.3. Both body size and ovariole number had significant effects on m.p.f. but these effects were different in the two morphs. While the food plants had significant influences on size and fecundity, these were relatively small. The m.p.f. of the small morph was 125.8±11.1 eggs, and of the large morph 318.7±8.3 (95% cl).4. Laboratory experiments on the flight performance of newly‐emerged midges indicated that the small morph was not dispersive and that about 80% of the large morph was dispersive. No differences in size, wing length or fecundity could be found between the two behavioural types of the large morph.5. The nature of the polymorphism is unusual, particularly since the dispersive individuals potentially have similar (or greater) fecundity than the non‐dispersive ones.6. Estimates of achieved fecundity (eggs actually laid, rather than m.p.f.) were 67.8±9.6 (field, minimum) and 138.9±30.4 (laboratory), the latter estimate being based on large‐morph females.