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Under favorable growth conditions cover crops are efficient tools to scavenge available nitrogen in the soil after the main crop and reduce nitrate leaching. However, their ability to reduce nitrate leaching is influenced by the available growth conditions after sowing and their characteristics to assimilate biomass and nitrogen (N). A flexible sowing time of cover crops without compromising their benefits to the environment implies knowledge of how the growth conditions after sowing of the cover crop affect leaching. Fodder radish, phacelia, and oats have different growth and N uptake characteristics, and their ability to reduce nitrate leaching depending on growth conditions after sowing may therefore differ. In this study, these three cover crops were evaluated, and their ability for taking up soil N and reducing nitrate leaching was quantified based on four sowing times from early August to early September with intervals of 7–11 days in 2019, 2020, and 2021 in Denmark. N uptake was measured in autumn each year and nitrate leaching measurements took place during the drainage period until the following spring. The N uptake decreased with subsequent sowing times across the cover crops and years. However, the decrease was different in different cover crops and different years. Nitrate leaching reduction also decreased with subsequent sowing times. On average, fodder radish reduced nitrate leaching by 64 kg N ha-1, significantly more than phacelia and oats with 47 and 44 kg N ha-1, respectively, across all sowing times and drainage periods. With an average reduction of nitrate leaching of 0.8 kg N ha-1 per day and no interaction of N uptake and cover crops, the ability of fodder radish, phacelia, and oats to reduce nitrate leaching was not significantly different. Fodder radish and early sowing was the most effective combination to obtain the maximum benefits of nitrate leaching reduction by a cover crop.

Parent-offspring communication is widely regarded as having evolved to provide the parent with honest information about the hunger state of its offspring, thus enabling it to mediate conflict over resource allocation between parents and offspring. The conflict is caused by the offspring benefitting from receiving more care than the parents are selected to provide due to the costliness of care. I studied the role of parent-offspring communication as a mediator for the conflict in the burying beetle Nicrophorus vespilloides. The burying beetle is an excellent study system for this question, as the larvae, that are raised on carcasses of small vertebrates and cared for by both the male and the female beetle, beg for food from their parents with highly distinguishable begging displays. First, I examined whether offspring adjusted their begging to different classes, or individual adult beetles. I found that while the larvae did not discriminate between male and female beetles, they adjusted their care to cues indicating individual recognition of adults. Second, I tested whether begging was based on offspring size at egg stage, and found no indication that offspring adjusted their begging to improve their innate quality. Third, I examined whether parental response to begging exhibits behavioural plasticity when the internal clock for the timing of reproduction for the parent, and the demand from the larvae do not meet. I found that the parents adjusted their care based on the amount of begging exhibited by the larvae. Fourth, I investigated whether parental adjustment of care based on offspring begging incurs a reproductive cost to them. I found that the females paid a cost in fecundity, but not in the number of dispersing larvae or their own survival. My original contribution to knowledge is therefore to show through these four studies, that offspring begging is adjusted based on parental cues, and can directly affect proximate parental behaviours, and also incurs a reproductive cost to their future reproductive success, thus providing more experimental evidence for the importance of parent-offspring communication, and its implications to the evolution of parental care.

Offspring begging can be triggered by a variety of acoustic, visual or chemical cues from the parents. In many birds, nestlings use information derived from these cues to discriminate between individual parents or different classes of adults. Although begging occurs in some insects, we know very little about discrimination between adults by insect larvae. Here, we examine whether begging larvae in the burying beetle Nicrophorus vespilloides can discriminate between individual parents or different classes of adults. We found that larvae showed no discrimination between male and female beetles, but that they begged more towards breeding beetles than towards non-breeding ones. These results were robust regardless of whether larvae had been reared in presence or absence of adult beetles, thus suggesting that larval discrimination is based on an innate template that requires no prior exposure to adult beetles. We also found that larvae begged more towards unfamiliar beetles than towards familiar ones, suggesting that they can learn to discriminate between individual parents based on cues about familiarity. We conclude that insect larvae may benefit from discriminating between different classes of adult beetles, as it allows them to lower the costs associated with begging in response to irrelevant environmental cues (costly in terms of wasted effort) and with not begging in response to the presence of caring parents (costly in terms of lost feeding opportunities).