Alternative reproductive tactics and the propensity of hybridization.

One explanation for hybridization between species is the fitness benefits it occasionally confers to the hybridizing individuals. This explanation is possible in species that have evolved alternative male reproductive tactics: individuals with inferior tactics might be more prone to hybridization provided it increases their reproductive success and fitness. Here we experimentally tested whether the propensity of hybridization in the wild depends on male reproductive tactic in Calopteryx splendens damselflies. Counter to our expectation, it was males adopting the superior reproductive tactic (territoriality) that had greatest propensity to hybridize than males adopting the inferior tactics (sneakers and floaters). Moreover, among the territorial males, the most ornamented males had greatest propensity to hybridize whereas the pattern was reversed in the sneaker males. Our results suggest that there is fluctuating selection on male mate discrimination against heterospecific females depending on both ornament size and the male's reproductive tactic.

Interspecific aggression and character displacement in the damselfly Calopteryx splendens.

Problems in species recognition are thought to affect the evolution of secondary sexual characters mainly through avoidance of maladaptive hybridization. Another, but much less studied avenue for the evolution of sexual characters due to species recognition problems is through interspecific aggression. In the damselfly, Calopteryx splendens, males have pigmented wing spots as a sexual character. Large-spotted males resemble males of another species, Calopteryx virgo, causing potential problems in species recognition. In this study, we investigate whether there is character displacement in wing spot size and whether interspecific aggression could cause this pattern. We found first that wing spot size of C. splendens in populations decreased with increasing relative abundance of C. virgo. Secondly, C. virgo males were more aggressive towards large- than small-spotted C. splendens males. Thirdly, in interspecific contests C. virgo males had better territory holding ability than C. splendens males. These results suggest that interspecific aggression may have caused character displacement in wing spot size of C. splendens, because the intensity of aggression towards large-spotted males is likely to increase with relative abundance of C. virgo males. Thus, interspecific aggression may be an evolutionarily significant force that is able to cause divergence in secondary sexual characters.

Immunocompetence, developmental stability and wingspot size in the damselfly Calopteryx splendens L.

Calopteryx splendens males exhibit a remarkable variation in wing pigmentation both within and between populations. In this study, we examined whether the wingspots of male C. splendens are related to male quality. We measured the nylon implant encapsulation rate for 85 males and found that males with larger wingspots had a faster encapsulation rate, indicating a better immunocompetence. We also found that the encapsulation rate was positively correlated with the density of haemocytes in the haemolymph. Another measurement of male quality, fluctuating asymmetry of wingspots, correlated negatively with the size of the wingspots. Males with asymmetrical wingspots also had lower encapsulation rates than more symmetrical males. Our results suggest that the size of wingspot is an indicator of male quality in C. splendens.

[Four cholera epidemics in nineteenth-century London]. / Lontoon neljä 1800-luvun koleraepidemiaa.

Asiatic cholera originated in India and spread to Europe in the early years of the nineteenth-century. In Britain the first cases were diagnosed late in 1831. The epidemic, reached London in February 1832. The authorities were poorly prepared for the invasion of a new epidemic and the doctors disagreed bitterly on the measures to be taken. There was little co-operation between the authorities, and the fact that the urban poor mistrusted the medical profession did not improve the situation. All this resulted in several cholera riots. These riots were not, however, as violent as those in several other cities in Europe. The 1832-33 cholera epidemic claimed 4,000 to 7,000 victims in London. It seems probable that several isolated cases of cholera occurred in London in 1852. It was not, however, until September 1853 that it was officially announced by the British authorities that a cholera epidemic was claiming victims not only in London but also in other parts of the country. During this epidemic numerous Londoners lodged complaints against nuisances in the metropolis. Yet, in most cases, the fines imposed on offenders were rather slight, since the authorities were extremely reluctant to interfere with anyone's trade or business. It was during this epidemic that John Snow, a London doctor, succeeded in tracing the epidemic to a single water pump on Broad Street in the Golden Square area. Snow did not, however, succeed in convincing the majority of his colleagues regarding the erroneous nature of the miasma theory during the epidemic of 1853/54, which cost the lives of some 12,000 people in the city area....