Phenotypic plasticity of senescence in Daphnia under predation impact: no ageing acceleration when the perceived risk decreases with age

Recognising the nature of the predation risk, and responding to it accurately, is crucial to fitness. Yet, even the most accurate adaptive responses to predation risk usually entail costs, both immediate and lifelong. Rooting in life-history theory, we hypothesize that an animal can perceive the nuances of prey size and age selectivity by the predator and modulate its life history accordingly. We test the prediction that—contrary to the faster or earlier senescence under predation risk that increases with prey size and age—under predation risk that decreases with prey size and age either no senescence acceleration or even its deceleration is to be observed. We use two species of indeterminate growers, small crustaceans of the genus Daphnia , Daphnia Pulex and Daphnia magna , as the model prey, and their respective gape-limited invertebrate predators, a dipteran, midge larva Chaoborus flavicans , and a notostracan, tadpole shrimp Triops cancriformis . We analyse age-specific survival, mortality and fertility rates, and find no senescence acceleration, as predicted. With this study, we complete the picture of the expected non-consumptive phenotypic effects of perceived predation pressure of different age-dependence patterns.

An updated and detailed taxonomical account of the large Branchiopoda (Crustacea: Branchiopoda: Anostraca, Notostraca, Spinicaudata) from the Yale North India Expedition deposited in the Yale Peabody Natural History Museum

We present an updated taxonomic account of a few of the large branchiopod species present in the collections of the Yale Peabody Museum of Natural History. Our study shows that the Artemia species in the collections is not Artemia salina given the presence of spines at the base of the penis and its frontal knob morphology. This population cannot be assigned to any particular species due to lack of comparative material of other Artemia species and therefore, now reduces the authentic distribution record of Artemia salina to just one in the subcontinent. The morphology of eggs taken from the Streptocephalus longimanus allotype is distinct from what has been described later by having lower number of polygons on the egg surface. The gross morphology of the Triops cancriformis from Punjab, Pakistan resembles those of the Kashmir population from India except for its larger size. Based on the morphological comparison, we show that Eocyzicus deterrana is indeed synonymous to E. hutchinsoni. This work further changes the total species tally of large branchiopods from 44 of the Indian subcontinent to 45.

First record of Triops strenuus Wolf, 1911 (Branchiopoda, Notostraca), a tadpole shrimp of Australian origin, from Japan

Three species of tadpole shrimp, i.e., Triops granarius (Lucas, 1864), Triops longicaudatus (LeConte, 1846) and Triops cancriformis (Bosc, 1801-1802), have been known from Japan. In this paper the author describes a fourth Triops species (= Triops strenuus Wolf, 1911) living in the rice paddies of a southern area of Honshu, the largest of the four main islands of Japan. This species was probably endemic to the Australian continent, and no habitat distribution outside Australia has been reported so far. The impact on the existing ecosystem of Japan is quite unknown, and therefore, it is necessary to announce this intrusion into Japan in order to clarify the invasion route, habitat ecology, and the future measures against this new alien species. This invasion is considered to be caused by the resting eggs brought together with silica sand (imported from Western Australia into Japan for the large-scale beach improvement). The results presented here also describe the phylogenetic relationship with all the Australian species described so far, but also all the known Triops species of the world, based on the nucleotide sequences of mitochondrial DNA.

A new molecular diagnostic tool for surveying and monitoring Triops cancriformis populations

The tadpole shrimp, Triops cancriformis, is a freshwater crustacean listed as endangered in the UK and Europe living in ephemeral pools. Populations are threatened by habitat destruction due to land development for agriculture and increased urbanisation. Despite this, there is a lack of efficient methods for discovering and monitoring populations. Established macroinvertebrate monitoring methods, such as net sampling, are unsuitable given the organism’s life history, that include long lived diapausing eggs, benthic habits and ephemerally active populations. Conventional hatching methods, such as sediment incubation, are both time consuming and potentially confounded by bet-hedging hatching strategies of diapausing eggs. Here we develop a new molecular diagnostic method to detect viable egg banks of T. cancriformis, and compare its performance to two conventional monitoring methods involving diapausing egg hatching. We apply this method to a collection of pond sediments from the Wildfowl & Wetlands Trust Caerlaverock National Nature Reserve, which holds one of the two remaining British populations of T. cancriformis. DNA barcoding of isolated eggs, using newly designed species-specific primers for a large region of mtDNA, was used to estimate egg viability. These estimates were compared to those obtained by the conventional methods of sediment and isolation hatching. Our method outperformed the conventional methods, revealing six ponds holding viable T. cancriformis diapausing egg banks in Caerlaverock. Additionally, designed species-specific primers for a short region of mtDNA identified degraded, inviable eggs and were used to ascertain the levels of recent mortality within an egg bank. Together with efficient sugar flotation techniques to extract eggs from sediment samples, our molecular method proved to be a faster and more powerful alternative for assessing the viability and condition of T. cancriformis diapausing egg banks.