Aufgabe 2 - Teilaufgabe 3 · Abitur NRW Biologie GK · Haupttermin · bilingual Englisch 2022

Material A: Ecology of Eurasian Shrews

The Eurasian water shrew 1 ( Neomys fodiens), the Mediterranean water shrew 2 ( Neomys anomalus) and the common shrew 3 ( Sorex araneus) all belong to the shrew family. All three species occur together in Europe and in parts of Asia.

The Eurasian water shrew is the largest of the three species. It has swimming bristles 4 on its hind feet and on its tail. It can swim and dive well. This nocturnal animal lives in thinner vegetation along the banks of fast-flowing rivers and streams. Swamps, wet forests and meadows are inhabited as well. The Mediterranean water shrew is also nocturnal and can also swim and dive. Its swimming bristles are shorter than those of the Eurasian water shrew and are sometimes missing entirely. It prefers to live on the banks of slower-flowing waters and in wetland areas with thick herb and bush growth. The diurnal and nocturnal common shrew occurs particularly in wet forests and meadows, but can also be found in other terrestrial habitats.

In addition to the invertebrates shown in Table 1, the Eurasian water shrew also preys upon smaller vertebrates such as frogs and fish. The common shrew occasionally eats small vertebrates such as frogs and young mice.

Table 1 Prey spectrum of the Eurasian water shrew, the Mediterranean water shrew and the common shrew. The faeces of captured shrews were analysed. The values show the percentage of shrews in which each prey animal type was found.

· Eurasian

water shrew · Mediterranean

water shrew · Common shrew

Terrestrial prey

Ground beetles · 22.6 % · 30.8 % · 6.3 %

Other beetles · 32.3 % · 38.5 % · 56.3 %

Beetle larvae · 6.5 % · 23.1 % · 31.3 %

Ants · 12.9 % · 0.0 % · 25.0 %

Millipedes · 61.3 % · 38.5 % · 3.1 %

Spiders · 74.2 % · 76.9 % · 63.3 %

Earthworms · 45.2 % · 100.0 % · 90.6 %

Aquatic prey

Caddisfly larvae 5 · 12.9 % · 15.4 %

Soldier fly larvae 6 · 6.5 % · 15.4 %

Asellus aquaticus 7 · 51.6 % · 23.1 %

1 Eurasische Wasserspitzmaus | 2 Sumpfspitzmaus | 3 Waldspitzmaus | 4 Schwimmborsten | 5 Köcherfliegenlarven | 6 Waffenfliegenlarven | 7 Wasserasseln

Material B: Prey Handling by Shrew Species

Shrews consume a large amount of food every day to meet their high energy requirements. As they are also active in the winter, they need food all year round. They often capture more prey than they consume directly; some of the prey animals are hoarded 8 for a while in their burrows 9. Some of these prey animals are bitten to immobilise them. This can be carried out mechanically by biting through nerves which innervate muscles. This immobilisation is also possible through the use of venoms.

The Eurasian water shrew and the Mediterranean water shrew produce a venom in glands under the tongue. The venom is transferred to the prey together with saliva and has a paralysing effect on the muscles. The common shrew, in contrast, is not venomous.

In a lab experiment, researchers investigated how the Eurasian water shrew and the smaller common shrew handle prey of different sizes and masses. The shrews were offered various prey animals: mealworms 10 were used as small, light prey, earthworms were used as medium-sized prey, and frogs as large, heavy prey. The proportions of the prey animals which were eaten either directly or little by little were determined, as were the proportions of prey animals which were either hoarded in the burrows or completely ignored (Figure 1A). Figure 1B shows the length of time needed to overpower the prey.

8 horten | 9 Bau | 10 Mehlkäferlarven

Material C: Relationships and Venomousness

The relationships between selected genera of shrew were determined based on molecular data; in a phylogenetic tree, these relationships are shown together with the occurrence of the trait 'venomousness' (Figure 2). The Eurasian water shrew and the Mediterranean water shrew both belong to the genus Neomys (Eurasian water shrews).

3. Analyse the phylogenetic tree shown in Figure 2 with regard to the presence of venom in the listed genera (Materials B and C). Drawing on all the materials, develop a hypothesis about how the Eurasian water shrew and the Mediterranean water shrew evolved (Materials A–C).

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