Magnetic and Electrical Properties of Ordered 112-type Perovskite LnBaCoMnO5+\delta (Ln = Nd, Eu)

Investigation of the oxygen-deficient 112-type ordered oxides of the type LnBaCoMnO5+\delta (Ln = Nd, Eu) evidences certain unusual magnetic behavior at low temperatures, compared to the LnBaCo2O5+\delta cobaltites. One observes that the substitution of manganese for cobalt suppresses the ferromagnetic state and induces strong antiferromagnetic interactions. Importantly, NdBaCoMnO5.9 depicts a clear paramagnetic to antiferromagnetic type transition around 220 K, whereas for EuBaCoMnO5.7 one observes an unusual magnetic behavior below 177 K which consists of ferromagnetic regions embedded in an antiferromagnetic matrix. The existence of two sorts of crystallographic sites for Co/Mn and their mixed valence states favor the ferromagnetic interaction whereas antiferromagnetism originates from the Co3+-O-Co3+ and Mn4+-O-Mn4+ interactions. Unlike the parent compounds, the present Mn-substituted phases do not exhibit prominent magnetoresistance effects in the temperature range 75-400K.Comment: 23 pages including figure

Signalling plasticity and energy saving in a tropical bushcricket

Males of the tropical bushcricket Mecopoda elongata synchronize their acoustic advertisement signals (chirps) in interactions with other males. However, synchrony is not perfect and distinct leader and follower roles are often maintained. In entrainment experiments in which conspecific signals were presented at various rates, chirps displayed as follower showed notable signal plasticity. Follower chirps were shortened by reducing the number and duration of syllables, especially those of low and medium amplitude. The degree of shortening depended on the time delay between leader and follower signals and the sound level of the entraining stimulus. The same signal plasticity was evident in male duets, with the effect that the last syllables of highest amplitude overlapped more strongly. Respiratory measurements showed that solo singing males producing higher chirp rates suffered from higher metabolic costs compared to males singing at lower rates. In contrast, respiratory rate was rather constant during a synchronous entrainment to a conspecific signal repeated at various rates. This allowed males to maintain a steady duty cycle, associated with a constant metabolic rate. Results are discussed with respect to the preference for leader signals in females and the possible benefits males may gain by overlapping their follower signals in a chorus

Broad- and narrow-sense heritabilities in a South African cloned open-pollinated Eucalyptus grandis breeding population

Genetic variances and heritabilities of a 66-month old cloned Eucalyptus grandis breeding population of families, derived from open-pollinated selections, were estimated. The genetic variance for the growth traits was largely additive genetic variance, whereas the proportion of non-additive genetic variance was notably higher for stem form and disease tolerance. A notably larger proportion of non-additive variance was observed for the growth traits and stem form among the F2 families. This is probably due to the reduction in additive variance through selection for general combining ability for these traits in the previous generations. No selection for disease took place in earlier generations and the proportion of non-additive genetic variance for this trait remains approximately the same for families of different generations.Southern Hemisphere Forestry Journal 2007, 69(2): 81–9

A comparison of deterministically predicted genetic gains with those realised in a South African Eucalyptus grandis breeding program

Tree breeders attempt to predict the genetic gains that are likely to be achieved through selection and breeding of new generations, using stochastic or deterministic modelling. There are many factors  that may cause a discrepancy between the predicted and realised genetic gains. Often the predictions for genetic gains are based on single trait selection, whereas in reality the breeding tends to be multitrait in nature. The violation of Hardy-Weinberg conditions, assumptions regarding outcrossing and relatedness, assumptions regarding the effect of the interaction between the  environment and the genotype, and numerous possible errors in the process of breeding, all could  result in unexpected discrepancies between the realised and predicted genetic gains. A series of genetic gains trials containing representatives of three generations of Eucalyptus grandis selections  were compared with the view to verifying the effectiveness of the E. grandis breeding program. Genetic gains of the F3 (third generation of pedigreed progeny) over the F2 generation (second generation of pedigreed progeny) were 15% for tree growth (volume). A comparison between F2 and P0 revealed an improvement of between 20% and 33% for growth. This exercise highlighted complexities of modelling the predicted genetic gains of assimilated genetic breeding trials. The predictions of genetic gains did deviate (in both directions) from those realised, although these deviations may be explained as functions of imperfect modelling. On average, however, the predicted genetic gains for tree volume over three  generations was 13% between generations,  whereas the average realised genetic gain in the genetic gains trial was 14%. It is therefore assumed that the E. grandis breeding population is indeed performing as expected, following classical tree breeding assumptions. Southern Forests 2009, 71(2): 141–14