Naida Zucker

MONTHLY REPRODUCTIVE CYCLES IN THREE SYMPATRIC HOOD BUILDING TROPICAL FIDDLER CRABS (GENUS UCA)

1. The degree of synchrony with which three tropical fiddler crabs, Uca musica terpsichores, U. latimanus and U. beebei, perform courtship, feeding and hood-building activities was studied.2. Courtship activities cycled on a monthly basis. Significantly more males of all three species courted during the week of the full moon when compared to the week of the new moon. Virtually no courtship occurred around the quarter moon periods. During peak courtship periods, 78% or more of the males of each species were displaying at the same time.3. Hood-building also peaked around the full moon and was performed only by courting males. Only a small percentage of courting U. beebei males built hoods, while virtually every courting U. latimanus male possessed one. An intermediate number of U. musica terpsichores built hoods.4. Almost all of the observed females were feeding. Wandering females (presumably sexually receptive) were observed almost exclusively during the same low tide hours in which males were courting.5. ...

The role of hood-building in defining territories and limiting combat in fiddler crabs

Abstract In Panama, courting males of three species of fiddler crabs sometimes construct semi-domes of mud (=hoods) over their burrow entrances. Males that do not construct hoods court in a circular area surrounding their burrow entrance. Males with hoods restrict their general activity and courtship to the semi-circular area in front of the hood opening. For Uca latimanus hoods appear to be an integral part of the courtship ritual and are constructed by all courting males. In the other two species, U. musica terpsichores and U. beebei , hood-building is associated with high population density and the presence of hoods reduces the frequency of combat among neighbouring males.

MAINTENANCE OF ANDRODIOECY IN THE FRESHWATER SHRIMP, EULIMNADIA TEXANA: ESTIMATES OF INBREEDING DEPRESSION IN TWO POPULATIONS

Abstract.— Androdioecy is an uncommon form of reproduction in which males coexist with hermaphrodites. Androdioecy is thought to be difficult to evolve in species that regularly inbreed. The freshwater shrimp Eulimnadia texana has recently been described as both androdioecious and highly selfing and is thus anomalous. Inbreeding depression is one factor that may maintain males in these populations. Here we examine the extent of “late” inbreeding depression (after sexual maturity) in these clam shrimp using two tests: (1) comparing the fitness of shrimp varying in their levels of individual heterozygosity from two natural populations that differ in overall genetic diversity; and (2) specifically outcrossing and selfing shrimp from these same populations and comparing fitness of the resulting offspring. The effects of inbreeding differed within each population. In the more genetically diverse population, fecundity, size, and mortality were significantly reduced in inbred shrimp. In the less genetically diverse population, none of the fitness measures was significantly lowered in selfed shrimp. Combining estimates of early inbreeding depression from a previous study with current estimates of late inbreeding depression suggests that inbreeding depression is substantial (δ= 0.68) in the more diverse population and somewhat lower (δ= 0.50) in the less diverse population. However, given that males have higher mortality rates than hermaphrodites, neither estimate of inbreeding depression is large enough to account for the maintenance of males in either population by inbreeding depression alone. Thus, the stability of androdioecy in this system is likely only if hermaphrodites are unable to self‐fertilize many of their own eggs when not mated to a male or if male mating success is generally high (or at least high when males are rare). Patterns of fitness responses in the two populations were consistent with the hypothesis that inbreeding depression is caused by partially recessive deleterious alleles, although a formal test of this hypothesis still needs to be conducted.

Anatomical evidence for androdioecy in the clam shrimp Eulimnadia texana

Recent genetic evidence suggests that the clam shrimp Eulimnadia texana exhibits androdioecy, a rare mating system. In this system, individuals are either hermaphrodites or males, pure females not being found. Through the use of light microscopy, this study provides anatomical evidence that egg-bearing individuals are, indeed, hermaphrodites. All such individuals observed possess ovotestes with testicular tissue restricted to the posterior region of the gonad. Developing sperms in hermaphrodites are similar in appearance to those seen in male-only individuals.

Courtship variation in the neo‐tropical fiddler crab Uca deichmanni: Another example of female incitation to male competition?

An unusual courtship pattern for fiddler crabs is described from field observations in Panama. This behavior pattern, referred to here as “directing,” differs considerably from the more frequently observed communal courtship system found in close relatives of Uca deichmanni. A male involved in “directing” approaches a female and attempts to carry or maneuver her into his burrow for mating. The female usually struggles to escape from the male. This activity often attracts other males which attempt to “direct” the female if she escapes from the first male. A male is most successful in “directing” a female into his burrow if a) he is larger than the female, b) the female is wandering (a sign of physiological receptivity) prior to the “directing” attempt, and c) several males attempt to “direct” the female at once. The results suggest that females are choosing mates by inciting several males to compete for them. The males which successfully “direct” the struggling females are probably the most fit males.

Delayed courtship in the fiddler crab Uca musica terpsichores

Abstract Courting male fiddler crabs of the species Uca musica terpsichores congregate in the upper central portion of the colony, while receptive females leave their burrows located at the colonys periphery and wander among the communally displaying males prior to choosing a mate. I observed that courting males in a newly-established population were significantly smaller than courting males in large high-density colonies. This observation led to a series of translocation experiments designed to ascertain whether high population density influences the size (=age) at which males begin to court. Smaller courting males from a low-density population failed to court after being placed among larger courting males in a high-density population. The reciprocal translocation revealed that smaller noncourting males from the high-density population would start courting shortly after being placed in a low-density population. Smaller males placed in the high-density population were subsequently observed significantly further away from where they were initially placed than were larger males similarly translocated. The results suggest that smaller males delay courtship activities once they are forced, via encounters with larger males, to the periphery of the colony. I believe that both intrasexual selection (competition from larger males) and intersexual selection (female choice of large males) are responsible for the delay in male courtship activities.

Selfing versus outcrossing in the androdioecious clam shrimp, Eulimnadia texana (Crustacea, Conchostraca)

The clam shrimpEulimnadia texana is an androdioecious crustacean in which hermaphrodites may self fertilize or outcross with males but cannot outcross with other hermaphrodites. Outcrossing is maintained within most populations of this species despite the high genetic cost of sex, suggesting that compensating factors provide an advantage to outcrossing. We hypothesized that one such benefit would be the production of larger clutch sizes resulting from outcrossed matings. To test this prediction, we recorded the body sizes and clutch sizes of hermaphrodites which mated via selfing or bia outcrossing. Clutch sizes showed significant, almost exponential, increases as body size increased in both selfing and outcrossing hernmaphrodites. The rate of this increase was the same for both groups, and there was no significant difference in clutch size when body size was controlled for between the two fertilization types.