When strontium-80 undergoes electron capture, it absorbs an electron, which results in a transformation of the element. Strontium has a mass number of 80 and an atomic number of 38. In the process of electron capture, one proton is converted into a neutron, effectively reducing the atomic number by one while keeping the mass number unchanged. This can be represented mathematically as follows:

Initial state: Strontium-80 (₈₀Sr, atomic number 38) + e^- → Final state: Rubidium-80 (₈₀Rb, atomic number 37)

Here, the mass number remains 80 (80 + 0 = 80), while the atomic number changes from 38 to 37 (38 - 1 = 37). Referring to the periodic table, the element with atomic number 37 is rubidium. Therefore, the daughter nuclide produced from the electron capture of strontium-80 is rubidium-80.