Output of tcpdump can be fed directly to Wireshark via:
$ tcpdump -s 0 -Un -w - | /Applications/Wireshark/Wireshark.app/Contents/MacOS/Wireshark -k -i -
And if tcpdump and Wireshark run on different machines one can do
$ tcpdump -s 0 -Un -w - | nc 192.0.2.1 8080
$ nc -k -l 8080 | /Applications/Wireshark/Wireshark.app/Contents/MacOS/Wireshark -k -i -
But I wonder if it's possible to initiate listening for a tcpdump stream from within Wireshark GUI (for convenience). I know that there is "UDP Listener Remote capture" that makes Wireshark to listen on a particular port for data of a patricular format. However, what format do I need to specify so Wireshark can interpret the tcpdump stream? I tried data, pcap and pcapng but it didn't work.