8 research outputs found
Male-like mudballing behavior of some female fiddler crabs (Uca tangeri)
At each low tide, male and female Uca tangeri
remove mudballs from inside their burrows and place them
on the surface. Previous studies have shown clear intersexual
differences in mudball arrangements. However, we
noticed that some females placed their mudballs in an arrangement
similar to that of males. In this study, we investigated
several factors that may have been responsible for
this change in female mudballing behavior. We found no
significant effect of the lunar cycle, female size and reproductive
state, or burrow features. We briefly discuss the
avoidance of sexual coercion or parasite modification of
host behavior as possible factors. Our study shows that
intersexual differences in mudballing behavior are more
complex than previously thought
Human exploitation of male fiddler crab claws: Behavioural consequences and implications for conservation
Male fiddler crabs have one of their feeding claws greatly enlarged, which may comprise up to 40%
of their weight. In southern Portugal (Ria Formosa) the major claw of the fiddler crab Uca tangeri
is a local delicacy. Fishermen break off the male major claw and throw the crab back into the mudflat
to regenerate a new one. Approximately 38 % of the males sampled had a missing or a regenerating
claw. Although individuals are not removed from the population the operational sex ratio is
biased towards females since other males and females behave towards clawless males as if they were
females. Moreover, removing the major claw from males prevents them from signalling (waving display)
to females to attract them to their breeding burrows and it also places them at a disadvantage
if they have to defend their burrows from males with intact claws. Thus, the harvesting of male fiddler
crab claws has potential consequences at the population level. In this paper we investigated these
potential consequences by comparing an exploited population of fiddler crabs at Ria Formosa with a
remote population at the Mira estuary that is not under human exploitation. The unexploited population
has significantly larger males and a significantly higher density of burrows. The operational sex
ratio is also significantly different between the two populations with a female-biased sex ratio in the
exploited population. These preliminary results suggest that claw harvesting in fiddler crabs has a
measurable effect at the population level. The consequences of this type of fishery in which the individuals
are not removed from the population but the population structure is potentially affected need
further investigation
Considerations on the use of video playbacks as visual stimuli: The Lisbon workshop consensus
This paper is the consensus of a workshop that
critically evaluated the utility and problems of video
playbacks as stimuli in studies of visual behavior. We
suggest that video playback is probably suitable for
studying motion, shape, texture, size, and brightness.
Studying color is problematic because video systems are
specifically designed for humans. Any difference in color
perception must lead to a different color sensation in
most animals. Another potentially problematic limitation
of video images is that they lack depth cues derived from
stereopsis, accommodation, and motion parallax. Nonetheless,
when used appropriately, video playback allows
an unprecedented range of questions in visual communication
to be addressed. It is important to note that most
of the potential limitations of video playback are not
unique to this technique but are relevant to all studies of
visual signaling in animals
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead
Intersexual differences in the mudballs of Uca annulipes (Decapoda: Ocypodidae)
This study investigated the features of mudballs produced by male and female Uca annulipes. Both sexes formed mudballs from mud excavated from within the burrow during the final hour of the low tide period. Males placed the centre of the mudball aggregation and the furthest mudball significantly further from the burrow than females. These observations suggest that the placement of male mudballs was not simply a by-product of burrow excavation
Chorusing by male european fiddler crabs, Uca tangeri: A study of visual communication netwoks
Chorusing behaviour, in which males aggregate and advertise to attract females, has been extensively studied in acoustically signalling orthopterans and anurans. Species which agregate and signal visually have comparanble behaviour but chorusing aspects has been studied infrequently. Male fiddler crabs (genus Uca) signal by waving and enlarged claw and form signalling aggregations, therefore, they have a potential to form a visual chorus. This study investigated the chorusing behaviour of male eurpoean fiddler crabs, Uca tangeri. The timing of waving by groups of three males (trios) was studied when each male was alone and when all three males were present. When waving in a trio, the male with the largest claw significantly increased the lenght of its interwave interval and some such males tend to wave soon after the other males. This pattern of waving may enhance the effectiveness of the large-claw males signal by avoiding visual object grouping and by allowing females to assess relative claw size more readily
Functions of mudballing behaviour in the european fiddler crab Uca tangeri
European fiddler crabs place mudballs around their burrow openings. Both males and females
placed mudballs, but there were major differences between the sexes in mudballing behaviour,
suggesting that the female’s mudballs were a by-product of digging out the burrow whereas the male’s
may have additional functions. When the male’s mudballs were removed experimentally, the number
and intensity of male–male agonistic interactions increased significantly. Experimentally visually
isolated males spent longer making mudballs and less time waving. In a binary choice test, females were
more likely to approach dummy males with mudballs, spent longer near these males and were more
likely to enter their burrows than dummy males without mudballs. The same pattern was apparent for
males with 30 rather than 20 mudballs. These results are consistent with a dual function for mudballs
in U. tangeri: to reduce the number and intensity of aggressive interactions between neighbouring males
and to attract females
The DNA sequence of the human X chromosome
The human X chromosome has a unique biology that was shaped by its evolution as the sex chromosome shared by males and females. We have determined 99.3% of the euchromatic sequence of the X chromosome. Our analysis illustrates the autosomal origin of the mammalian sex chromosomes, the stepwise process that led to the progressive loss of recombination between X and Y, and the extent of subsequent degradation of the Y chromosome. LINE1 repeat elements cover one-third of the X chromosome, with a distribution that is consistent with their proposed role as way stations in the process of X-chromosome inactivation. We found 1,098 genes in the sequence, of which 99 encode proteins expressed in testis and in various tumour types. A disproportionately high number of mendelian diseases are documented for the X chromosome. Of this number, 168 have been explained by mutations in 113 X-linked genes, which in many cases were characterized with the aid of the DNA sequence