Filial cannibalism and reproductive success in the maternal mouthbrooding cichlid fish Pseudocrenilabrus multicolor

Summary Pseudocrenilabrus multicolor is an iteroparous maternal mouthbrooding cichlid fish living in small and shallow waters in East Africa. It is subjected to large seasonal variations of population density. Laboratory experiments show that with increasing density and time after spawning the number of offspring present in the mouth decreased. By experimentally varying density and the numbers of fertilized and unfertilized eggs in the mouth at the end of spawning the following causes of brood size reduction were identified: (1) At high densities some of the spawned eggs are stolen by conspecifics before they are taken into the mouth. Of the eggs taken up a considerable proportion is unfertilized. (2) Unfertilized eggs are selectively swallowed from day 2 to day 5 after spawning. (3) Some of the fertilized eggs are also swallowed during mouthbrooding. (4) If the number of eggs in the mouth falls below a critical value of approximately 20% of the number of eggs spawned, they are all swallowed. By contrast, predation by conspecifics is insignificant as long as the brood is in the mother's mouth. The causes and functions of the mother's filial cannibalism are discussed.     

Temporal patterns in the vibratory courtship signals of the wandering spider Cupiennius salei Keys.

Summary The vibratory courtship signal generated by abdominal and leg movements of male Cupiennius salei on plants consists of impulses, which in groups of about ten form syllables. A syllable together with the preceding silent pause is called a sequence. Up to 50 sequences chained together form a series. A series together with the preceding silent period is called an interseries. A complete courtship is built up from a row of successive interseries. An additional signal produced by palpal drumming only occurs between syllables. Females respond to ca. 40% of the male signal series with a single irregular signal produced by leg oscillations and lasting for 113–1790 ms. Their response reduces the duration of the male interseries significantly from an average of 27.9 s to 20.6 s. The female signal follows a male signal series within a narrow time frame of 0.89±0.53 s. Analysis over long periods of time and of complete courtships showed the male signalling to be highly structured in the time domain and to contain many cues potentially usable by the female for both such precise timing and conspecific recognition: (1) On average, the interval between the last two syllables is significantly longer than the preceding ones. (2) During the course of a series, syllable durations increase nearly linearly from 93 ms to 123 ms. (3) The twelfth sequence (T-12) prior to the final one (T) is outstanding since here, roughly 4 s before the end of a series, the duration of sequences and pauses, the signal amplitudes and the occurrence of palpal drumming abruptly start to increase. Also, the frequencies contained in the syllables shift to higher values. (4) Between sequences T-4 and T-6 pause duration and sequence duration reach their minimum whereas the values for signal acceleration and the occurrence of palpal drumming are highest.     

Ökologische Situation der Region Leipzig-Halle

The deposition of heavy metals bound to air dust and their ecological effects depend, to a large degree, on particle size, which influences the transport processes in the environment. To estimate the size range of the particles mainly taken up by the pine needles, concentration gradients along a sector leeward of Leipzig were modelled according toGauss plume calculations. The results show that the aerodynamic size is between 1 and 10 μm. Particles of this size range can be taken up by lungs and, thus, have a particular toxicological relevance.     

Assessing the microbial activity of soil samples,its nutrient limitation and toxic effects of contaminants using a simple respiration test

Eight soil samples from five wells of a former gas plant site differing in the contamination with BTEX and PAHs as well as the nutrient content were investigated by soil respiration measurements. The basal, glucose as well as NH4+ and PO4(3-) induced cumulative oxygen consumption and carbon dioxide production in 72 and 120 h were determined and additionally the maximal turnover rates and the limitation quotients were calculated. Without additional carbon source only one of five investigated samples was clearly nutrient limited. After glucose supplementation four of seven investigated samples showed nutrient limitation that was in accordance with the available ammonium and phosphorous content. BTEX and PAHs did not exhibit an inhibiting effect on the respiration rate. In contrast, BTEX containing samples exhibited the highest oxygen consumption indicating biodegradation of the contaminants. The results show that oxygen consumption and carbon dioxide production as well as the kinetic of these processes are all informative parameters characterizing the whole microbial respiration potential and their nutrient limitation in soil samples. Therefore this fast respirometric method can be used for the decision if further detailed studies of the bioremediation are useful and if nutrient supplementation is recommended to enhance natural attenuation.